Hell, they're entirely the reason he's president today. Joe Biden did nothing of note in Iowa, New Hampshire and Nevada in 2020. Black votes in South Carolina bailed out his sorry primary campaign.
Yes, 90% will vote for Joe. But as enthusiasm drops, their willingness to actually vote goes down too.
I think you are right about the black vote. sadly. They are so conditioned that when it comes to actually pulling the lever, few will be able to rebel and do it for Trump. The Hispanic vote is different and far more amenable to change, so there’s that to look forward to.