Going to resource packs menu then clicking done causes resource reload, but only for every time you launch the game. This has been tested on Minecraft 1.21.3 with Fabric API 0.107.0.
This bug is separate from MC-264307 as I have mentioned that the issue in Fabric API is that it happens every time you launch the game.

I can reproduce this in 1.20.4

Is this issue separate from a similar vanilla issue that also causes resource reloading when clicking the 'Done' button?

Is this issue separate from a similar vanilla issue that also causes resource reloading when clicking the 'Done' button?

different from vanilla one, as [Mod] Greymagic27 said in the mojang one:

I was able to reproduce this only when I've first loaded up the game and went there. It displayed the red Mojang loading screen for 2 seconds or so.

After that I couldn't reproduce without relaunching again, and then it only did it once.

so it is separate from the Fabric API one in how it works because the Fabric API one is every time launch the game

When entering the resource pack screen, the game will disable resource packs that have been registered through fabric api, thus when pressing done it will reload the resources. If you re-enable the resources that were already enabled, the resources won't reload.

From my testing, this seems to happen no matter the activation type.

I am currently using fabric-api 0.97.3+1.20.5, with fabric loader 0.15.10, on 1.20.5-pre4, but this issue has been happening throughout the 1.20.5 snapshots.

Now checked on 1.20.5, still same issue

1.20.6 is also affected (API ver 0.97.8)

Happens with 1.21, loader 0.16.0 and fapi 0.100.7
doesnt matter if pressing "Done" or "esc", it will reload resources even if unchanged

also having this issue on 1.21.1