Yes, I thought about the option of creating a separate playlist, but it's not very convenient to update it manually all the time. But I just found another way, I cloned Poweramp and added the folders I needed there. The downside is that you have to make changes to the settings in both apps, but I don't change them that often.
It would be nice if this feature was implemented to be able to hide individual tracks/artists/folders from All Songs (yes, that sounds a bit crazy) because it's sometimes inconvenient to switch many times the tracks that are not relevant to the list, like in my case or podcasts.