Hello,
Mac 10.15.7 is Catalina ? Sorry for the late reply. But Airem = one person and I'm currently working on another games...
1) I can prepare a new update (1-3 days) and You will check if it's OK (I think on ITCH.io I can upload versions for MAC 10.15.7) if there is still an error you have to ask for a refund or I will send you a key for another game
2) You can also run IMPOSSIBLE in a different way, but you must write to me at info@airem.pl
3) Or show this post and ask for a refund How are refunds handled - Questions & Support - itch.io
Let me know what are you going to do?