I've literally exhausted every single potential fix--- removing all the white spaces from icon names, checking the index.theme file and rewriting it to reflect the directory structure (it's wrong as is), removing and trying to rebuild the icon cache, literally everything. I have no clue what else to do. The icons themselves work fine out-of-box but there are many icons that are straight up missing or not being displayed correctly (i've attached my taskbar as an example). I truly don't know what else to do.
Distro: Linux Mint 22.1 x86_64
Theme: Windows-XP-Royale [GTK2/3]
Icons:Windows-XP-3.1 [GTK2/3]

Here is how I changed the index.theme file (as a txt file).
themeindex.txt