What Graphics card model is it? Have you tried updating the graphics card drivers from the manufacturer? Often, old drivers are not compatible with Photoshop. Also, if it is a really old card then it could be that card is no longer supported too.
You may want to contact Adobe support and tell them you want your PGU enabled in the preferences and see if they can fix it. Don’t mention Pixnub though. The online chat support in India is really good about looking for excuses to close the case. As soon as they hear “3rd party plugin”, some of them are quick just to send you away and tell you to talk to the plugin developer, even for issues that are clearly Photoshop. So just focus on the GPU, not on SPA when you talk to Adobe. You can tell them you need the Face Aware Liquify tool in Photoshop. That won’t work without the GPU. If they get that to work then SPA will work too.
or you can just buy a Mac M1 mini and all of you problems would be solved 🙂