Let me clarify:
Indigo 2022.1 runs equally well on all versions of macOS since 10.12 (Sierra). We install our own Python 2 and Python 3 on ALL macOS releases, and it doesn't use any Apple-installed version (either preinstalled or installed from Xcode). It does not interfere with the built-in Python 2 install on earlier macOS releases, it just ignores it.
Python 2 (old) plugins will still run (mostly, there are a couple that may not so check with the developers or other users of those plugins). It will also run new Python 3 plugins.
Finally, if something happens and one has determined that they can't run Indigo 2022.1 to their satisfaction, it's easy enough to just shut down 2022.1 completely and then restart 2021.2.