I'm not sure if this is a bug or a feature request, but I can't find a way for a character to add spells to or cast spells from spell storing items like ring of spell storing or ioun stone of reserve from their character sheet. This makes it tricky to use the items.

Yeah, that's not possible with older items. They were working on updating items that had set specific spells and charges, but I don't think they finished that work, and definitely not for items that let you attach any spell. What you want to do is create a feat that lets you add spells, then name it the same as the item.

There is no way currently to add spells to stuff like that. Your best bet for items like the ring is to make a homebrew of the item and attach the spell to that, and for stuff like the Artificer feature to make a homebrewed magic item for it as well. If you need it I can help you as I’ve already made them for myself.