August 23, 2020 8:34 EDT PM
I use to use TuneUp religiously. It was really good but since Apple Music subscriptions came I abandoned my library for Apple's even though I was using ALAC (Apple's FLAC if you will) files.
That being said their site is still up, http://www.tuneupmedia.com but I haven't used my lifetime subscriptions in years. I remember that toward the 'end' the version of the app was problematic and I had to revert to a lower version to make things work again.
As you may know, TuneUp was actually accessing music databases on your behalf, they weren't the database themselves but they had a useable UI to deliver your music tags to a database for comparison and come back with updates to the tags your music held.
For me, TuneUps really strength was finding music album covers rather effectively.
Alternatives to TuneUp that I would consider are https://picard.musicbrainz.org. I use to use musicbrainz and it was really very good. I use to use it even while using TuneUp. It wasn't as easy to use all those years ago and I found myself having to restore a music backup as it kind of mangled things up somewhat. In other words it seemed too liberal with its judgement. I would definitely consider it but there may be a learning curve but who knows, I used it years ago.
I found another Mac only app called https://2manyrobots.com/yate/ YATE. I have no experience with it but they have a trial.
In both cases, back up your music before having either of these modify your music tags.
Hope this helps but why not just use Apple Music, unless of course you have lossless audio tracks which Apple hasn't yet embraced other than offering a free lossless algorithm, aka ALAC. Of course, one thing I can't stand about Apple Music is that it doesn't work with https://audirvana.com which is something I really truly miss, it gave music a 'stage' that I have never experienced before. I have only used Audirvana with lossless music files and the quality was breathtaking. It puts Apple Music to shame in terms of audio quality, it literally puts it to shame.
Look, I know I offered you more than you might want to chew on but I hope those TuneUp alternatives find you well.