Oh that sucks. I hope the maintainers read this thread.
The best course of action is (1) to try to find help on the mailing list for new functions to ease the migration to the new syntactic rules (there is one already in the release notes) and (2) to raise your voice on the mailing list and support those who share the same view.
I've been a release manager for 9.0, not the real maintainer, so things may have slipped in directions I didn't have time to carefully review. If I manage to get involved again as a real maintainer, I will enforce syntactic stability and backward compatibility as much as possible.
What might be nice is, for every release, to provide a script that would update your org files to the current standard.
Maybe such files even exist, but they would need to be closer to the users' hands.
In anycase, it must be said that many of us simply could not stay organized without efforts like yours, and we're greatly appreciative! (couldn't write a grant without it anymore)
New Org linter library
org-lint can check syntax and report common issues in Org documents.