There’s a 100% chance that his mic issues are not driver related, but instead are Discord’s fault. They are classically awful at providing feature parity for Linux.

Have him fiddle with the audio settings, it’s probably either the echo cancellation or noise reduction. As another commenter mentioned there are third party solutions for both.

FYI for GW2 you can actually use the steam client even if your account is non-steam, you just need to use a launch option – see here https://www.reddit.com/r/Guildwars2/comments/wvxqe3/logging_into_guild_wars_2_on_steam_with_an/

To be clear, the vast majority of “games with anti-cheat” work perfectly well on Linux. It’s just the ones where developers have chosen to either explicitly block Linux (e.g. Fortnite) or to use invasive rootkit anti-cheat (e.g. Riot games, FACEIT, etc.) which wouldn’t be allowed to work on Linux anyway because it’s a really stupid idea to let random gaming companies have access to your ring 0.