The core rules of d&d (mechanics but not settings) are available under a free license (it was the Open Gaming License, or OGL, although I have a feeling it’s a different license (Creative Commons , maybe?) now following the backlash from earlier this year when Wizards tried to scrap the OGL and replace it with a worse license)
Pathfinder was originally based on the d&d 3.5e ruleset. I’m not sure how far it has diverged from that, as I’ve played neither. Solasta is based on d&d 5e (the latest version of the rules), but is in a non-d&d setting of their own creation. BG3 is also based on 5e (although less strictly than Solasta), but also has the D&D license, so can use the Forgotten Realms/Sword Coast setting
Personally, I enjoyed Solasta, and think it’s a great representation of combat on 5e. The writing and story aren’t amazing, and it lacks the crazy amount of freedom/choices of BG3, but mechanically, it’s a great implementation of 5e rules.
My issue with it is that it really doesn’t feel like morrowind in space to me. Morrowind had some interesting environments, and most places you found had some environmental storytelling going on. I loved morrowind because exploring felt interesting (but combat was bad)
Here I’m finding the environments uninteresting, with a few exceptions there seems to be little in the way of environmental storytelling and exploration doesn’t seem that compelling. I’m enjoying the combat more than the exploration, which is unexpected for a Bethesda game. It feels like they’ve gone for quantity over quality with environments, and things are so far apart in fairly uninteresting planets that I feel like it’s just a bit of a chore.
Maybe I’ve just been unlucky with the world’s I’ve explored, and I’m enjoying it enough to keep playing a bit more in the hope it improves, but so far, it’s not what I was hoping for.