[13:40:18] [Worker-ResourceReload-11/WARN]: Texture minecraft:block/inv2 with size 1x1 limits mip level from 4 to 0
[13:40:18] [Worker-ResourceReload-11/WARN]: minecraft:textures/atlas/blocks.png: dropping miplevel from 4 to 0, because of minimum power of two: 1

I haven't investigated much, I'm running modded 1.20.1 with lots of resource packs, however the visual issue appears once I enable this resource pack. With shaders it's no problem, however without is pretty harsh looking at QHD resolution. I suggest remaking the inv2.png with resolution 16x16.

Edit: It seems like Optifine can work around this, however the vanilla renderer and Sodium can't (or won't). So it is not reproducible on Optifine.

If I miss some additional info, please let me know! I'm hopeful that this opened issue is helpful overall to your resource pack.

I have looked around and found that the repository contains correctly sized textures, however after extraction from the published archives shows that the files have been modified. This is where I learned about PackSquash.

I have tried to test the changes on a fork, however I am not familiar with Github Actions and I didn't want to accidentally do something, so I couldn't test it, however I made a pull request #26 .