What changed?

I've been backing up my phone regularly. ios 15.6 and catalina 10.15.6. Today, when I tried to back up again, I got the message that I must update my mac software to back up my phone! But why? I haven't changed anything. I am updating to 15.7 and hope that fixes it. What happens when I can't update my computer anymore? I don't want to buy a new one as long this old one does everything I need. Seems to me apple is overboard on security sometimes.