Windows applications that register their protocol just work when this is done;

wine start urihere
umu-run start urihere

I'll add this to heroic games launcher soon, would be cool if it was added to protontricks

Somewhat related PR;
https://github.com/Heroic-Games-Launcher/HeroicGamesLauncher/pull/5682/changes

Application examples for uri testing;
magnet: - deluge (use old deluge-2.0b1-win32-setup.exe for testing if you can as it tends to run better with wine?)

irc://irc.libera.chat/#linux - hexchat

brawlhalla mod loader (bmod) - https://gamebanana.com/tools/20722, https://gamebanana.com/mods/677353