bog posted above:
"Retroactive has been discontinued, and does not support macOS Sequoia or later."
I'm posting from my 2018 Mini, currently booted to the latest developer beta of Sequoia.
Here's a screenshot I took a few minutes ago, with iTunes running, via Retroactive, alongside the "About This Mac" window:
Does this convince you?
Be aware: I don't use anything more with iTunes, other than the free "streaming internet radio" tuner, which Apple chose to discontinue with the "Music" app...
(it's possible that there are other features of iTunes that no longer work via Retroactive, but again, I use only the radio tuner)
I launched Retroactive 2.0, and it offered to upgrade to 2.1.
When I ran 2.1, it said Retroactive was now discontinued, but when I dismissed that alert, it STILL offers to install iTunes.
So... I'm going to GUESS that the reason the developer chose to discontinue it may be that even modified versions of Aperture will no longer work right with Sequoia, perhaps the same for iPhoto.
But... iTunes looks like it will still install and work -- for now.
So my advice to the OP stands -- if you don't care for Music, but liked iTunes, you might still be able to use it via Retroactive.
At least... worth a try.