Newpipe remains one of the best solutions for background playback. They do tend to move pretty quickly to patch "fixes" that YouTube throw in now and again. It's also useful for video backups if you need to preserve them for any reason.
I am using Tubular, a NewPipe fork that has built-in SponsorBlock and ReturnYouTubeDislike features.
Lately I discovered Firefox with background play and sponsor block extensions still work. If this stops working hopefully tubular will be a good backup.