By my reading I would allow a Maverick to cast a breakthrough spell into a Ring of Spell Storing and for that spell to remain stored even if the Maverick changes breakthroughs. The spell will be removed from the ring when it is cast. HOWEVER… (1/2)

Thanks for the insight! And thank you so much for creating my favorite class in dnd, and subsequently creating its most fun (IMO) subclass in 5e.

… As a DM, I might impose a duration on Find Steed when it is cast indirectly, such as through a scroll or Ring of Spell Storing. Find Steed is a weird blend of spell and class feature; when acquired in this way I might say the steed only sticks around for a day, or maybe a week.