These bugs are fixed in one of the latest proton-cachyos dev builds, which means a future stable version of proton-cachyos might contain the same solution to the bugs I experienced.
I can't post a link that leads to more context, because I don't have 1 reputation, but I can say you'll find it in the proton-cachyos GitHub repo by searching for "[Compat]: Plutonium COD WAW Main Menu Music Stops Playing and Game Freezes When Loading Map".
That's issue #236 in that repo.
