user6542: Where can I find the list of supported boards in Arduino IDE 2.0 without installing the IDE? Googling it was not fruitful. Specifically, I'm looking for ESP32-S3 support.

user88218: 
Where can I find the list of supported boards in Arduino IDE 2.0
Specifically, I'm looking for ESP32-S3 support.

Without knowing what you want to do, the short answer is: check this JSON's "boards" properties: https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json.
The Arduino IDE is just a user interface on top of the arduino-cli. It provides a way to change the board_manager#additional_urls property of the CLI configuration. Once a new 3rd party platform URL is specified in the IDE, the CLI will see the available boards of the platform. You'll need to install the platform to verify and upload your sketches. After installing the platform, the "boards.txt" will be available on your filesystem for the CLI. For this example, this is https://github.com/espressif/arduino-esp32/blob/master/boards.txt.

user70020: The 2.X IDE makes use of arduino-cli:

The backend operations such as compilation and uploading are offloaded
to an arduino-cli instance running in daemon mode.

which has roughly the same internals as arduino-builder

The arduino-builder is now just a wrapper of arduino-cli

which is what the 1.X IDE uses to launch the build process. Roughly speaking, they support the same boards.
About the only difference I've noticed is that the 2.X IDE does not yet support disableRTS and disableRTS board properties, so some ESP32 board that require these settings will not (yet) work in with the 2.X IDE's serial monitor. The ESP32-CAM-MB together with ESP32CAM is one combination where the Serial Monitor won't work. You can still upload with it though.
So, the IDE should compile and upload for your ESP32-S3 just fine. If you want to know whether or not the Serial Monitor will work, it's down to looking at the specific board schematic to see whether or not the EN/RESET and GPIO0 signals are connected to the serial transceiver using only diodes. The official boards don't do this. So if you have one of the Expressif devkits (or a clone) the 2.0 IDE Serial Monitor will work fine with it.

6542: <p>Where can I find the list of supported boards in Arduino IDE 2.0 without installing the IDE? Googling it was not fruitful. Specifically, I'm looking for ESP32-S3 support.</p>
 88218: <blockquote>
<p>Where can I find the list of supported boards in Arduino IDE 2.0
Specifically, I'm looking for ESP32-S3 support.</p>
</blockquote>
<p>Without knowing what you want to do, the short answer is: check this JSON's <code>&quot;boards&quot;</code> properties: <a href="https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json" rel="nofollow noreferrer">https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json</a>.</p>
<p>The Arduino IDE is just a user interface on top of the <code>arduino-cli</code>. It provides a way to change the <a href="https://arduino.github.io/arduino-cli/latest/configuration/" rel="nofollow noreferrer"><code>board_manager#additional_urls</code></a> property of the CLI configuration. Once a new 3rd party platform URL is specified in the IDE, the CLI will see the available boards of the <a href="https://arduino.github.io/arduino-cli/latest/platform-specification/" rel="nofollow noreferrer">platform</a>. You'll need to install the platform to verify and upload your sketches. After installing the platform, the <a href="https://arduino.github.io/arduino-cli/latest/platform-specification/#boardstxt" rel="nofollow noreferrer"><code>&quot;boards.txt&quot;</code></a> will be available on your filesystem for the CLI. For this example, this is <a href="https://github.com/espressif/arduino-esp32/blob/master/boards.txt" rel="nofollow noreferrer">https://github.com/espressif/arduino-esp32/blob/master/boards.txt</a>.</p>
 70020: <p>The 2.X IDE <a href="https://github.com/arduino/arduino-ide" rel="nofollow noreferrer">makes use</a> of <a href="https://github.com/arduino/arduino-cli" rel="nofollow noreferrer">arduino-cli</a>:</p>
<blockquote>
<p>The backend operations such as compilation and uploading are offloaded
to an arduino-cli instance running in daemon mode.</p>
</blockquote>
<p>which has roughly the same internals as <a href="https://github.com/arduino/arduino-builder" rel="nofollow noreferrer">arduino-builder</a></p>
<blockquote>
<p>The arduino-builder is now just a wrapper of arduino-cli</p>
</blockquote>
<p>which is what the 1.X IDE uses to launch the build process. Roughly speaking, they support the same boards.</p>
<p>About the only difference I've noticed is that the 2.X IDE does not <em>yet</em> support <code>disableRTS</code> and <code>disableRTS</code> board properties, so some ESP32 board that require these settings will not (yet) work in with the 2.X IDE's serial monitor. The ESP32-CAM-MB together with ESP32CAM is one combination where the Serial Monitor won't work. You can still upload with it though.</p>
<p>So, the IDE should compile and upload for your ESP32-S3 just fine. If you want to know whether or not the Serial Monitor will work, it's down to looking at the specific board schematic to see whether or not the EN/RESET and GPIO0 signals are connected to the serial transceiver using only diodes. The official boards don't do this. So if you have one of the Expressif devkits (or a clone) the 2.0 IDE Serial Monitor will work fine with it.</p>
