Edit: Samsung Keyboard (in the personal profile) was reinstalled probably after a system update and was the culprit. The issue is now solved. Thank you for your comments.
I have made a work profile using Shelter. I was copy-pasting some stuff in my personal profile while the work profile was disabled. Later, I discovered everything I had copied was showing up in Samsung Keyboard’s clipboard history (in the work profile). Personal profile’s Samsung Keyboard was uninstalled via ADB (among some other packages like Google Play Services). What package could be the culprit? (I’d love to just install LineageOS on it but there isn’t a built for the device yet. I just don’t use it for sensitive stuff.)
Samsung’s keyboard history is sketchy as. Even when you select everything and ‘delete’ it from the history you can STILL PASTE. Like dude. I know some people find keyboard history useful but I don’t want it, just a huge security risk.
clipboard history is different from the system clipboard. it works the same way on kde plasma, probably windows too. it depends on the keyboard on android to clear it from the system clipboard too, it seems the samsung keyboard devs did to bother with this