I'm trying out modpacks with certain recent versions of Minecraft, for example Minecolonies Official v2.6 with MC 1.16.4 and the game loads but without any sound.
The modpack works fine with MultiMC launcher.
My suspicion is that sound assets are not downloaded by this new beta launcher. Possibly for certain MC versions. Because some other modpacks with older MC versions do work (e.g. Compact Claustrophobia with MC 1.12).
I tried to clean up everything by deleting the Minecraft folder and CurseForge settings, basically reinstalling and reconfiguring everything from scratch but I got the same result.