Hi Moonlight -

Not so much a "learning" but here's a resource to jam.

Check out the "Quartet 1" app in the App Store or their website https://www.quartetapp.com/ .  It's an app with a truckload of not so subtly disguised "clones" of famous jazz tune.  You can change the key and tempo on the fly, and pull up piano, guitar, and uke (of all things...) chords.  You can also change the backing combo on most tunes (piano, anyone?). It's a little clunky but is a great collection of background tunes for jazz jamming.  I think I bought it for $3 US when they first released it.  Not sure of the current price but I'm betting it'll be worth it for you.

This is a good bet if you're looking to jam to a hundred or so jazz standards.  You can find your favorites here and jam to your hearts content.

If you're looking for a custom/composer style thing, this group of developers also makes a number of other "studio style" back up apps called "Session Band".  I have the blues app and plan to get their other offerings which includes "Session Band Jazz1".  Price is currently less than $10 US for each of the "Session Band" apps. Definitely not perfect, but I believe their apps allow you to export to Garage band.  All of the music is royalty free, so you can use it as a base for your own recordings if you you wish.  https://www.sessionbandapp.com/  Looks like they have a half dozen or so jazz apps.

I'm not affiliated with these guys, but I was looking for back-up loops to jam against and ran across these apps.

Hope it helps,

Rumble