Unable to download apps on iPhone 12 Pro

You should use just one Apple ID. You cannot transfer purchases to a different Apple ID so you need your old ID if you want the purchase you made with it.

Click on this link to read what to do "If you forgot your Apple ID password" --> https://support.apple.com/HT201487

or go directly to this link --> http://iforgot.apple.com/

Also read about "What to do after [or before] you change your Apple ID email address or password" - https://support.apple.com/HT204071

If you still need help:

Contact Apple for help with Apple ID account security "This article provides country-specific Apple Support contact information for customers seeking help with their Apple ID password or other security-related issues." --> https://support.apple.com/HT204169

You can try setting up Family Sharing between the IDs if you want to be able to share purchases made with the IDs.

Family Sharing.         

Family Sharing - Set up.       

Yes, yes, you can use Family Sharing. I didn't bother mentioning it because frankly the main issue appeared to be the forgotten password and once you have the old ID working and the new one isn't that new then you might as well just stick to the older ID. Managing two IDs can be a hassle.

The only way to avoid the wait is to remember the password and sign in.

Only what I posted above.

Not that I know.

Please note that most people posting here do not work for Apple, we're just unofficial volunteers, users like you, trying to help others.

We can tell others what they need to do to help themselves. :-)