Shield Proficiency with Feats

[ProsecutorGodot]

A part of design that is never explicitly stated but is heavily implied with each instance is that a character should have Medium Armor proficiency to have proficiency with Shields. To my knowledge, there is no way to get shield proficiency without also getting medium armor proficiency, and I'm pretty sure its intentional.

I would generally avoid giving casters who don't get this proficiency by default the ability to do so with less downside than Multiclassing. That's just my opinion though, the only classes this benefits are Wizard, Sorcerer, Warlock (who aren't hexblade) and Rogue.

a wizard or sorcerer wanting to drop a whole ASI into being able to use shields might as well get a few melee weapons too to enable their warmage concept.

I can't help but be cynical here and assume its a player who wants to maintain their full caster progression (or doesn't want to delay their spell level progression) and cut the usual feat cost for keeping that progression.

I would sooner recommend multiclassing into Cleric, then depending on the choice they can also get heavy armor proficiency.