Friends lvl 4 fighter can't take Magic Initiate: Wizard. He's able to select the feat, select the cantrips/spell, but cannot click accept. I tried as well, taking over his character, and it did not work. Seems like this is a bug?
Were they both custom characters? Maybe it's an issue with custom characters not being able to take that feat. Also, the Warlock and the Cleric deviations don't work either.
Haven't been able to complete the level up process with any of the magic initiate feats selected with a character/class that doesn't already have spell slots.
With Lae'zel as a fighter/battle master, I can't successfully pick any of the magic initiate feats. However with Lae'zel as a fighter/eldritch knight I can complete the level 3 to 4 process any of those three feats. Similar results for Asterion as a rogue/thief vs rogue/arcane trickster.
Can confirm, my Battle Master Lae'Zel cann't take Magic Initiate: Wizard. I was really looking forward to trying that once I found a magic circlet that set the wearer's Intelligence to 18.