Version?

1.21.1 Neoforge

can you check other guis? like many many of them , you should see similar seams there in those too

if you press f3+s it should save the atlas textures in the screenshot folder. now theres nothing special about how the altas rendered, just like other guis. however theres this issue called atlas bleeding that might occur on some system. the way it works is that textures near the atlas might bleed into eacnother. if thats the case so, by looking at that gui atlas textures that is saved there you shouldsee which sprites those 2 strips belong to as they are right below shears and pin. Similarly other gui sprites that have another one right below without transparent edges should be affected just as much

Not a single GUI I've seen has had this issue (but I'll check and report back)

Update: checked EVERY SINGLE GUI of every modded and vanilla block, and even scrolled through a bunch of config and vanilla menus, literally the Map Atlas is the only thing that has this tearing

It looks like the textures below the pin are 3 different ones, two for some kind of UI button and another for a furnace type block. For the shears it's a letter and a lock. I have no clue from which mods they belong to I won't lie. Is there a way for me to fix this issue myself?

So not really this is atlas bleeding and should affect all texture on the atlas. Ones near their neighbor bleed into them. Thing is as far as I know it just happens on some systems and gpus

Damn, so another L for Intel GPUs then. God I need a new computer

This stuff is nee as they just added the gui atlas on 1.21. thing is this should happen on all sprites, those are nothing special so other sprites with neighboring stuff should also have bleed. Maybe it's just more noticeable in mine given they are mostly transparent on edges