OK I see the problem now: I was stupidly copying and pasting from the PDF manual that only shows a somewhat misleading invocation of git checkout to bring out the correct tag. The manual suggests:
The git cloned repository contains all the NXP releases. To work with a different release, the git tag command shows
available releases and git checkout <tag name> is used to move to that version.
lf-5.15.32-2.0.0
For example, choose lf-5.15.32-2.0.0 snapshot: $ git checkout -b lf-5.15.32-2.0.0
Well, any competent git user knows that it should be:
git checkout tags/lf-5.15.32-2.0.0
after I started using brain to type the correct git command, everything is nominal.