I was restricted to my MacBook Air when I was in hospital, and that has the same specs as a 500USD Mac mini (m4, 16GB RAM). It plays 3D stuff like Valheim at 60FPS! The only issue is the more limited library compared to my Linux and Windows machines.

For £500 you are doing a lot more than pong. I am kinda curious how far back you have to go at different price points to play the majority of games from that era. Pretty sure £500 is still doing a lot of games 10+ years old.

Retro gaming on a Pi comes in at £50 or so, depends on which one you get though as more RAM does cost more. Downside here is ARM might limit your options a bit for some things not quite so old but it probably would otherwise be powerful enough for. Box86 + wine exists but that looks too much like 2010 Linux gaming that I would rather leave in the past. Some open source games could be compiled on it too.

Pi Zero could run a few games too and that is like £15. But your choices are going to be very limited for anything beyond retro gaming. CDDA should compile and technically run, slowly. Got a pinephone which has similar specs and can do it but compiling takes about an hour and I found out the game had loading screens I wasn't even aware of before trying to run it on specs like that.

Even a lot of modern indie titles will play on a low-spec PC.

Mame and pre-2001 gaming FTW!