I've had my 13 mini for 27 months, and its battery capacity is 70%. Less than 2 months ago, it was 76%, so it's falling quickly! I use optimized charging, and I use corded charging nearly all the time.
Nevertheless, because I usually don't have to go more than 4 hours or so between charges, it's not that big of a deal yet. About the only concern is that if the charge falls to 15%, it can shut off unexpectedly.
(If you're wondering why I don't replace the battery: if that were the only issue, I would. But it also has a crack in the screen, and FaceID doesn't work in the sun. I've learned the latter is nearly unheard of, so I'd like to replace the whole phone. If 13 minis reappear in Apple's refurbished store, I'll buy one.)