Sadly nothing’s will fix the damage. As someone already posted you best bet is to stop causing damage and let your hair grow out. Adding protein can help fill in some of the “holes” to help you hair feel and look better but it doesn’t undue damage. (No hair mask will actually undue damage, you best bet is to hide it). I used to use henna powder on my hair once a month to make it feel smoother and fuller after dying it. Mix henna powder with just enough water to make a paste, add some oil and honey. Don’t let the past sit unless you want to dye your hair red! Put it in right away and then wash it off after an hour. Henna will release red/orange pigment if anything acidic, like lemon juice, is added to it so just keep that in mind.
This may sound like an insane idea, but have you ever thought of just shaving it off and starting over again? With Covid happening now and the fact that you can’t really go anywhere, it may not be the worst idea? This way, your hair can grow nice and healthy and have a fresh start. And you can get yourself a wig until the hair starts growing back again. I have a friend that did this a few years ago, and her hair grew SO quickly and was very healthy. Anyway, I know it’s a crazy suggestion, but just thought I’d throw it out there 