I use two mobile phones, a Fairphone 2 and a Samsung A3 2016. Both run with Lineage and F-Droid as app store. Google apps are not installed.
I noticed that the scope of apps in F-Droid is slightly different on both phones. For example, I have some issues with the A3 and I want to install alogcat (root) to record log files. On the Fairphone 2, the app is available. On the A3 it is not (only alogcat without root). I already checked the settings but I was not able to find any difference that would fade out the app.
@4nndee Can you enable the archive repo in fdroid on both phones and compare the apps again? The phone that already has an app installed will always show it as available even when it has been moved to the archive,
Also there was a bug which was only fixed a few days ago that app which were removed (or moved to the archive) were never removed from the local copy of the app-index. So this also might explain what you are seeing.