Purchases and subscribed services are available to you on your Apple ID account as used to buy or subscribe. These services are not available to other Apple ID accounts, and these properties cannot be transferred to other accounts.
When you stop and resubscribe for the Apple TV+ subscription, then that has no consequences for purchased movies.
I recently changed my Apple ID …
One could have changed the name (email address) for an Apple ID account, without creating a new account. Then all the purchases and subscriptions would have stayed with it. Change your Apple ID - Apple Support
You don’t mention why you did change it, so I can’t say if that would have been a proper solution to your situation.
Doesn’t seem fair. They were bought, not temporarily rented, by same person (me)
These purchases are still available to you … on your old Apple ID account.
One possible workaround is to have both accounts in a Family Sharing group with Purchase Sharing active, although that is more complicated that just using the original Apple ID.