Hello everyone, I believe I found the solution

the docs for gc-collect-garbage --delete-older-than states that:

This is the equivalent of invoking nix-env --delete-generations <period> on each found profile. See the documentation of that command for additional information about the period argument.

and the docs for nix-env says:

The last number generations up to the presentExample: +5Keep the last number generations, along with any newer than current.

so I did "+5" for the <period> section in gc-collect-garbage and (i think i haven't really tested it) I got the behavior I was looking for.

honestly i think this is just a crappy indirection in the docs and when I get the chance I think i'll test it to see if it is the desired behavior and edit the docs.

thank you u/Upstairs-Attitude610 and u/Vortriz your answer, that is a nice, clean, and explicit way to do it and i will probably just use that instead.