Q: cant change region on App Store after cancelling apple music membership

Hello there, TanBrar.

It seems you're unable to change Country on your App Store because you still get a message that you have to cancel Apple Music, even though you have already done so.  The following Knowledge Base article provides some clarification on how the process of cancelling Apple Music completes:

Manage your Apple Music membership on your iPhone, iPad, iPod touch, Mac, or PC

Turn off automatic renewal to cancel your membership

If you want to cancel your Apple Music membership, turn off Automatic Renewal.

Your membership might renew if you don't turn off Automatic Renewal more than 8 hours before your renewal date.

On your iPhone, iPad, or iPod touch

1. In the Music app, tap your profile icon in the upper-left corner.
2. Tap View Apple ID. You might need to sign in.
3. Under Subscriptions, tap Manage. If you have more than one subscription, tap Your Membership (Apple Music Membership) to see your membership options.
   
4. Under Renewal Options, turn off Automatic Renewal. Confirm your selection, then tap Done.
   
   If you don't see the option to turn off Automatic Renewal, your subscription will automatically stop at the end of the current billing cycle.
5. Tap Done to return to your Account screen, and then tap Done to return to the app.

As shown in the image and description in Step 4, the subscription stops at the end of the billing cycle. After that date, you should be able to proceed with changing your App Store:

Change your iTunes Store country or region

Thanks for reaching out to Apple Support Communities.

Kind Regards.

Hello again, TanBrar. 

You are very welcome. I hope the information was helpful in explaining your concern.

Sincerely.