There are more ways to handle this, but since you are talking about single tracks versus album tracks, it would make sense to remove (blank) the 'album' tag from all singles.
(if they even have 'album' populated to begin with?)
Then create a library filter with the rule: Album has no value.
And another one: Album has a value.
@hiccup: Thanks for your Idea,
but if I understand it correctly I would have to go through all the songs individually to edit the "album tag info". I admit that I don't really understand how to do this in practice since my library is very large, which I don't think is a big deal now. I prefer psychoadept's solution as it seems automateable to me.
You can also use the Album Track Count built-in virtual tag for this, which is the number of tracks in your library from that album. So, if Album Track Count = 1, you know it is a single. You might need the Additional Tagging and Reporting Tools plugin for this, but you can also compare Album Track Count to Track Count (total tracks on the album). So even if you have 2 or 3 tracks, if it's not the whole album you'll catch that.
I have researched the virtual tagtopic, but unfortunately it is too complex for me, I do not understand how to implement your advice in MusicBee.
Can you please tell me the steps how I can implement it in MusicBee.
Maybe you can make a screenshot or screen recording, so you don't have to write so much because of me.
That would be really great. Thank you both for your support.