Upgraded from iPhone XS Max to 13 Pro Max - How to Keep Wipe Old Phone Without Removing from New

I think I found the answer here: What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support

It seems that manually deleting content (photos, messages, etc) will delete them from new phone

You shouldn't manually delete your contacts, calendars, reminders, documents, photos, or any other iCloud information while you're signed in to iCloud with your Apple ID. This would delete your content from the iCloud servers and any of your devices signed in to iCloud.

Remove your personal information from your old device

If you paired an Apple Watch with your iPhone, unpair your Apple Watch.

Back up your device.

Sign out of iCloud and the iTunes & App Store. 

If you're using iOS 10.3 or later, tap Settings > [your name]. Scroll down and tap Sign Out. Enter your Apple ID password and tap Turn Off.

If you're using iOS 10.2 or earlier, tap Settings > iCloud > Sign Out. Tap Sign Out again, then tap Delete from My [device] and enter your Apple ID password. Then go to Settings > iTunes & App Store > Apple ID > Sign Out.

If you're switching to a non-Apple phone, deregister iMessage.

Go back to Settings and tap General > Transfer or Reset [device] > Erase All Content and Settings. If you turned on Find My [device], you might need to enter your Apple ID and password. If your device uses eSIM, choose the option to erase your device and the eSIM profile when asked.

If asked for your device passcode or Restrictions passcode, enter it. Then tap Erase [device].

Contact your carrier for help transferring service to a new owner. If you aren't using a SIM card with your device, you can contact them to get help transferring service to the new owner.

Remove your old device from your list of trusted devices.

When you erase your iPhone, iPad, or iPod touch, Find My [device] and Activation Lock are turned off.