I've actually kept postponing upgrading to Catalina (I'm still on Mojave) because I want to keep iTunes. I have a lot of stuff there I don't really want scattered all over the place, and I always felt iTunes was underrated.
[1]: https://forums.macrumors.com/threads/itunes-12-6-5-3-on-maco...
I'm in a similar position, having several music apps I bought a while ago that won't work in Catalina. But I have to upgrade because it's my development machine. So far my plan is to upgrade my MacBook Pro to continue develop software, and leave my Mac Pro with Mojave to compose music. I wonder how others deal with this.