@nomadic Thanks mate! I knew it must already be a thing, cause like, duh, toolbars are customizable, why can't context menus be! And even searched in Settings... Should have googled/bing-ed too. You saved the day, mate.
Thx for your reply.
I am indeed using different "Reading lists" addons and I am still trying to find the "good" one. I never tried the one you posted, it seems good and simple at the same time. The fact it has not been updated since 2018 could be a problem though...
In any case, if the great Vivaldi Team can do these modifications to their native feature, it would be better 🙂