FAT32 does not support file ownership, that is why you are getting an error when you try to change it.
Based on certain evidence, I am guessing you do not historically mount your drives with the terminal. Since something changed recently as you mentioned, I wonder if you have seen this solution? Hard Drives No Longer Mounting On Startup - #8 by BluishHumility
That person also lost their Automount settings when they took the update to Plasma 5.25 (I’m only guessing on your Plasma version, since no garuda-inxi).