When I make banana mini-muffins, I wind up freezing most of them and they're great right out of the freezer. Bigger muffins might need a bit of defrosting to avoid being hard to bite into.
The chocolate zucchini bread I was making last summer was pretty good straight out of the freezer, too. (I didn't plant any zucchini this year, in part because we got tired of finding things to make with them last year, and most of those recipes wouldn't be very keto-friendly.)