I believe that VKD3D can give you directx support. Proton should be able to run most games these days, which is essentially a bundle of wine + vkd3d and other things. This is what valve created to run games on steam on linux/steamdeck. https://www.protondb.com/ shows what is able to run on it and it is most things that do not have some form of incompatible anticheat.
You might have more luck not using wine directly (if that is what you are doing) and using things like steam (you can add external games to it to run them in a proton context) or lutris or heroic games launcher.
Almost. But with one key difference. PPAs are precompiled binaries where you cannot inspect the source - you have to trust the maintainer of the PPA. AUR is a repository of source packages which you can download and inspect yourself (or hope others have done this). This makes AUR more community focused than PPAs I feel. AUR is also a central repo managed by people that dont own the vast majority of the packages hosted on it and where packages can be taken down if found malicious. PPAs are lots of separate repositories all managed by different people that generally maintain all the packages for their PPA.
Though in both cases anyone can upload anything to them, so they are not 100% trustworthy. But I do think the way AUR works puts them ahead of PPAs.