The errors are:

ERROR: /Users/runner/work/alire-index/alire-index/index/index.toml: index version (1.3.0) is newer than that expected by alr (1.2.1). You may have to update alr

I guess it is something with the imminent release and using the rc1, but I don't know what should I do to fix it. Maybe use the beta, as the last time, or doing it manually; so I'll wait for advice.

Submissions against index version 1.3.0 are not yet working; the branch exists but it is not the default. If you reopen against base branch stable-1.2.1, it should work.

Ah, but your crate requires 2.0. Then I'd say just wait until it gets released, as we don't plan on having a devel index branch that would allow testing this in advance to release.

In fact, my original idea for this tool was to use this command for the installation in an AppDir directory:

alr exec -P -- gprinstall --prefix=AppDir --create-missing-dirs --mode=usage -f

But after alr install I thought it would make more sense to simply use that feature. Now I'm wondering if supporting Alire 1.x with that command after a failed attempt to run alr install would make sense. I guess the result would be the same.

Yup, our gprinstall call looks pretty much the same, so using that should work too.