system
A chat on subreddit /r/pcmasterrace
human
Windows 11 requires I think 8th generation or newer. When you're looking at intel systems

i3 slowest 

i5 mid level 

i7 fastest mainstream 

i9 super high end

The next this is the generation that is the number after the i 3/5/7/9, in your example i7 2xxxx is how everyone is able to know it's old, it's telling us it's a very early generation, given the current one is 13 and they come out once a year.

Aim for an i5 10 or better, the main thing to consider is the graphics card though. Eg i5 10xxx where the X is some numbers. Don't worry too much about getting an i7, the graphics card is the most important component for games.  

Nvidia has generations as well


10 

16 (mini generation that's between 10 and 20)

20

30

40( this is very new and currently extremely expensive as it only has top end cards. Probably should ignore them on your budget) 


Aim for a 20 at least the second pair of numbers is the type of cars in that generation is the tier these go from 50,60,70,80,90. So for example a 2050 is the slowest card in the second generation, aim for a 3060 if you can. But a 2070 would be great too. Avoid anything 10 or 50. 

The only other thing to make sure is that it has a solid state drive, this will say SSD, M.2 followed by the capacity, the higher the better, anything over 500 is good, ideally over 1T or you might have to juggle some games in and out depending on which ones you want to use and how gig they are

Hope this helps. For context a new pc (no monitor or keyboard etc) with i5, a 3060, 1TB of storage should cost about £900 -£1000 so if you go second hand bare that in mind
gpt
Also worth mentioning 16 series Nvidia cards. Which were released after 20 series and have rasterizing performance similar to a 10series of 1 class higher. So a 1660 is similar to a 1070. They lack any raytracing or dlss though.