user76819: I've been trying to follow the official Arduino instructions on how to program and power an external breadboard, and I've gotten a pack of ATmega328p's that may or may not have been preloaded with the bootloader (found here). From the title, I assumed that they were, in fact, preloaded, but I followed the instructions to "reload it" from a working Arduino (with its original microcontroller), and I did it with the following circuit setup (this is the best image that I have of it, unfortunately, I promise I've checked that the wiring actually is equivalent to the original diagram, just shifted around for convenience on the breadboard):

I'm not sure whether I should've kept the original microcontroller in, as the guide ambiguously shows a void in the area where the controller should be in the provided diagram...

...but my thinking was that the Arduino basically isn't anything without its attached microcontroller, so attempting to "send" bootloader code to a separate microcontroller would require a plugged in microcontroller, and that was the only way I got it to work.
With all this set up, I tried to test using this new microcontroller, and it worked perfectly when mounted in the provided microcontroller area. However, when I tried to follow this up with the steps detailed in the guide, found here, with the following circuit (slightly better angle):

...I was faced with errors of being unable to connect.

From what I understand, it seems like the Arduino should automatically detect that no microcontroller is plugged in, hence allowing the stated "FTDI chip can talk to the microcontroller on the breadboard instead" from the guide. However, the error I'm getting seems to be the same as the error I got when I just plainly tried to send code or program without any microcontroller connected, so I'm assuming this implies that it can't find any microcontroller, either internal or standalone.
From googling this error, it seems that others have had this problem with seemingly no solution, and I have absolutely no idea how I could fix this. If there's something I'm missing, would greatly appreciate the help.
side note, when I was idly testing out the program with a tiny test circuit that lights up an LED, after programming it with a program that turns on a GPIO pin, connecting that pin to the LED, it did in fact light up. I'm concluding this means that the setup of the actual microcontroller is functional, but it's unable to be written to. this has also happened with the original microcontroller that I tried to simply program externally.
any help is appreciated, thanks for reading!

user31043: In the case of using an Arduino as a USB/UART (FTDI) adapter to upload a sketch onto a barebones Arduino (ATMEGA328P) via its own bootloader,  a reset of that MCU chip must preceed the sketch upload. That is because, immediately following the reset, the bootloader watches the serial traffic to see if this is marked as a sketch upload and, if so, processes it. If this reset operation fails, for example through a bad or missing connection, the sketch upload attempt will also fail.
A good description of the sketch upload process can  be found here: https://www.instructables.com/Overview-the-Arduino-sketch-uploading-process-and-/

76819: <p>I've been trying to follow the official <a href="https://docs.arduino.cc/built-in-examples/arduino-isp/ArduinoToBreadboard" rel="nofollow noreferrer">Arduino instructions</a> on how to program and power an external breadboard, and I've gotten a pack of ATmega328p's that may or may not have been preloaded with the bootloader (found <a href="https://www.digikey.com/en/products/detail/universal-solder-electronics-ltd/ATMEGA328P-PU-Arduino-Bootloader/16822123" rel="nofollow noreferrer">here</a>). From the title, I assumed that they were, in fact, preloaded, but I followed the instructions to &quot;reload it&quot; from a working Arduino (with its original microcontroller), and I did it with the following circuit setup (this is the best image that I have of it, unfortunately, I promise I've checked that the wiring actually is equivalent to the original diagram, just shifted around for convenience on the breadboard):</p>
<p><a href="https://i.stack.imgur.com/M0l4b.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/M0l4b.png" alt="enter image description here" /></a></p>
<p>I'm not sure whether I should've kept the original microcontroller in, as the guide ambiguously shows a void in the area where the controller should be in the provided diagram...</p>
<p><a href="https://i.stack.imgur.com/qPZNg.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/qPZNg.png" alt="enter image description here" /></a></p>
<p>...but my thinking was that the Arduino basically isn't anything without its attached microcontroller, so attempting to &quot;send&quot; bootloader code to a separate microcontroller would require a plugged in microcontroller, and that was the only way I got it to work.</p>
<p>With all this set up, I tried to test using this new microcontroller, and it worked perfectly when mounted in the provided microcontroller area. However, when I tried to follow this up with the steps detailed in the guide, <a href="https://docs.arduino.cc/built-in-examples/arduino-isp/ArduinoToBreadboard#uploading-using-an-arduino-board" rel="nofollow noreferrer">found here</a>, with the following circuit (slightly better angle):</p>
<p><a href="https://i.stack.imgur.com/WtIeI.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/WtIeI.png" alt="enter image description here" /></a></p>
<p>...I was faced with errors of being unable to connect.</p>
<p><a href="https://i.stack.imgur.com/AAoxd.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/AAoxd.png" alt="enter image description here" /></a></p>
<p>From what I understand, it seems like the Arduino should automatically detect that no microcontroller is plugged in, hence allowing the stated &quot;FTDI chip can talk to the microcontroller on the breadboard instead&quot; from the guide. However, the error I'm getting seems to be the same as the error I got when I just plainly tried to send code or program without any microcontroller connected, so I'm assuming this implies that it can't find any microcontroller, either internal or standalone.</p>
<p>From googling this error, it seems that others have had this problem with seemingly no solution, and I have absolutely no idea how I could fix this. If there's something I'm missing, would greatly appreciate the help.</p>
<p>side note, when I was idly testing out the program with a tiny test circuit that lights up an LED, after programming it with a program that turns on a GPIO pin, connecting that pin to the LED, it did in fact light up. I'm concluding this means that the setup of the actual microcontroller is functional, but it's unable to be written to. this has also happened with the original microcontroller that I tried to simply program externally.</p>
<p>any help is appreciated, thanks for reading!</p>
 31043: <p>In the case of using an Arduino as a USB/UART (FTDI) adapter to upload a sketch onto a barebones Arduino (ATMEGA328P) via its own bootloader,  a reset of that MCU chip must preceed the sketch upload. That is because, immediately following the reset, the bootloader watches the serial traffic to see if this is marked as a sketch upload and, if so, processes it. If this reset operation fails, for example through a bad or missing connection, the sketch upload attempt will also fail.
A good description of the sketch upload process can  be found here: <a href="https://www.instructables.com/Overview-the-Arduino-sketch-uploading-process-and-/" rel="nofollow noreferrer">https://www.instructables.com/Overview-the-Arduino-sketch-uploading-process-and-/</a></p>
