f-droid no longer provides an option to enable the archive repo. It also won’t allow you to add it with either qrcode or manually. I have a Galaxy S4 with Lineage Android 11 installed.
This is about repositories not an app.
Kindly read again. The response has stated how to enable archive repos.
Edit: Just rechecked myself.
F-Droid App > Settings > Repositories > Enter F-Droid Repo > Click Settings > Toggle Archive repo option.
Let it refresh or manually trigger refresh. Done.