Micha, from what I see at
https://nvb.meertens.knaw.nl/populariteit/naam/Micha, is used more for boys at a rate of almost 20:1... It's a judgement call, but I feel that is probably enough to label as masculine only. Please understand I'm not trying to say it's not sometimes used by girls, and I'm certainly NOT saying it shouldn't be used by girls. I just want to provide the best snapshot of usage that I can.