Your GPU was released in 2011, you could try and force Photoshop to use the GPU, assuming you're using the most recent version that is.
You need to create a PSUserConfig.txt file with the following entry and save it to the location mentioned in this link
# Force GPU On
Photoshop's core functions are being rewritten to use Metal and Direct X GPU calls instead of the old Open GL/CL.
The current system requirements are for a GPU that supports Direct X 12 which the 7900 does not. Whilst you may be able to restore some functionality by forcing your GPU as shown by Ged, this may still give crashes and unexpected behaviour. If it works, treat it as a workaround that buys a bit of time, but the real answer is an up to date card.
Thank you! Upgrading to RX 570 soon, looks like it supports directx 12. In the meantime, I can deal with a slightly unstable ps.
You could downgrade to v.20.2 in the meantime. It's the last version that will recognise my V7900.
Sorry, v.22.2 of course.