Not if you’re following that! Mostly I just dump them in ~/.icons, and then select them in Appearance. Occasionally I find them as package in the AUR, and just install them with yay. Both work, so far always. I have sometimes run the command to create an icon cache, but it’s been pretty hit-or-miss. No problems so far.
I suspect this isn’t a whole lot of help! What icons are they, and whence are they sourced? Can only guess without that I guess…
I managed to understand that the default directory for moving the themes in Endeavour (perhaps in other distros as well) is currently the /usr/share/themes, which should also be system-wide. Moving the themes there and doing a fast “shutdown -r now” seemed to have solved out everything.