I often see four things I personally think of as fairly distinct conflated in discussions of redemption arcs
a) Does the would-be former villain actually want to be redeemed? Are they capable of going through life without resorting to evil coping mechanisms? Are they willing to make any relevant reparations?
b) Are the people likely to be interacting directly with the ex-baddy willing to forgive and forget/begrudgingly decide they’re useful enough to be worth it/throw a party because they’re delighted by the convert? Are their former compatriots in evil (if they have them) going to come along with them into the light, try to kill them over the betrayal, or embark on a campaign to lure them back to team ne’er do well?
c) Is society at large likely to accept the heel-face turn? Are they going to the magical space hague? Is there a magical space hague? Are we talking shunning, 1000 years dungeon, execution, or like, star fleet summer camp community service? None of the above because war criminals who defect at the right moment get ice cream and a new name? None of the above because zombies ate the justice system? None of the above because zombies eating the justice system would be an improvement on the justice system?
d) Is redemption something the audience actually wants to see from that character?
and these are just not the same thing! All you really need for a redemption arc is a! b-c give you an outline of what that redemption might plausibly look like, and d is a market research question. You can argue about whether some characters are beyond redemption, or if it’s believable that they’d decide they want to be better, or it’s plausible that they’d be given the opportunity to make meaningful reparations, or whether redemption is possible without that opportunity, but the basic seed of a redemption arc is just a person who wants to be better than they are choosing to act in accordance with that desire.