I tried some addons and probably cookie is not only form of data. As I was loggined on piped.video but there were no cookie showing in quick cookie manager I also used cookie auto delete and piped data was not deleted. I dont have technical details but in an addon (Name was probably something like forget forever) which claim to delete all site data. There were about 10 types of data listed including cookie,IndexDb,Session storage etc. That extension was also not able to remove that data (Was showing not available on your platform).