Advancement Screen: custom background texture not loading (json format changed?)

i have a datapack with custom advancements and custom advancement tabs. these tabs use a custom texture as their background image which is called blank.png and is simply just no texture at all. the root.json for all advancement tabs have the background component included that point to skyquest:textures/block/blank.png. this used to work in 1.21.4, after upgrading to 1.21.5 it doesnt work anymore. i dont know what changed or how to fix and i assume its just some formatting that changed