Possibility #1:
Video RAM is damaged.

Possibility #2:
Your CPU is too fast.

this seems to be a 2d issue to start with. Check the legs on the chips.

The gpu gets pretty hot stock, if you haven't experienced one before it feels like its overheating when its not

Looks like it might be a couple of stuck data lines to memory. The first line on your boot screen says "A'a"d M/d%l!r B O " which should read "Award Modular BIOS". Looking at the hex values for the ASCII codes:

1w 77h, ' 27h
2r 72h, " 22h
3o 6fh, / 2fh
4u 75h, % 25h
5a 61h, ! 21h

So both 6 and 7 get changed to a 2. In binary that's 110 and 111 getting changed to 010. The spaces for the missing I (49h) and S (53h) probably get changed to control codes 09h and 03h.

failing solder joints in 3dfx cards is very common those days

snufkin wrote on 2022-10-21, 10:54:

Looks like it might be a couple of stuck data lines to memory. The first line on your boot screen says "A'a"d M/d%l!r B O " whi […]
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Looks like it might be a couple of stuck data lines to memory. The first line on your boot screen says "A'a"d M/d%l!r B O " which should read "Award Modular BIOS". Looking at the hex values for the ASCII codes:

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1w 77h, ' 27h
2r 72h, " 22h
3o 6fh, / 2fh
4u 75h, % 25h
5a 61h, ! 21h

So both 6 and 7 get changed to a 2. In binary that's 110 and 111 getting changed to 010. The spaces for the missing I (49h) and S (53h) probably get changed to control codes 09h and 03h.

Thanks for noticing. I guess this means a faulty memory chip? If so, any idea how to identify it?

My guess, as rasz_pl suggested, would be that it's more likely to be a soldering problem than a faulty chip. Try booting up a few times whilst pushing on different chips and see if the display changes. Hot running BGA devices sometimes have problems with solder balls cracking (the original PS3 suffered from this with the 'yellow light of death'), so the problem may be with the GPU, so try pushing on that first. If it is that then some people have had success with just putting the card in an oven for a bit, but I've never tried that. I did have a go at a quick fix on a PS3 once by using a hot air gun to just reflow the balls for the main chips. It worked for a couple of months but then failed again. The proper fix is to remove the chip, clean everything up, re-ball the chip and then reflow it.