Ok, thanks. There is a cadabra2 available via apt-get, but it doesn't appear to work. It's described as: Cadabra 2.3.6 (build private dated 2022-01-31). AFAICT it can't find python where it expects to see it and then crashes.
I'll go ahead and try cadabra2-2.4.0-ulyana.deb from the Mint Ulyana 20 link on the download page, unless you would suggest something different.
For what it's worth, the python I'm using came from the repo.anaconda.com archive. I've currently got Python 3.8.5 and it's in /usr/local/anaconda3/bin/python, just in case there's some dependency there.