Illustrator v24.0.2
I don't know what triggers this, but sometimes there's error in selection that causing the object to be highlighted and can't deselect it by clicking outside artboard with selection tool.
This is getting frustrating. I really hope Illustrator get a renewal just by rebuilding the program from scratch without changing the initial tool since the bug is just too much.

workaround :
If the object is a grouped object, then double click it to enter isolation mode, and double click again to get out.
If not, then, save and close and re-open the document.