Yeah I had to lookup what I posted on reddit a while ago since I forgot the details.
So the problem was not fdroid, fdroid did not have the app at all. The problem was the izzyonfdroid repo which did not have the 64bit version and was not planning to.
Which in the end just leads me to using obtainium to get updates for this particular app. There were a couple like that. I can see them greyed out in droid-ify when scrolling, showing me I cannot install them, no version compatible with my device.
That's weird. When I look up Libretube I can find it in my f-droid app. Says it needs Android 5.0 or higher, maybe your version is too old so you cannot see it?