The key is going to be the PSU and looking at the pictures of the board and the back I don't think it's a standard ATX PSU. According to this thread on Tom's Hardware some versions are 12 volt only - you need to look inside and see if the main power connector is 16 pin or 20 pin. Hopefully it's the latter.
If you can upgrade the PSU, I'll echo @Tetras' recommendation of the RX 6600 and variants, maybe the 7600; if you cannot upgrade the PSU then I would not purchase a RX 6600 as you'll be stressing the PSU.
If you can upgrade the PSU, I'll echo @Tetras' recommendation of the RX 6600 and variants, maybe the 7600; if you cannot upgrade the PSU then I would not purchase a RX 6600 as you'll be stressing the PSU.