That is a very good question. The best you could do on iOS 16 would be to mark the photos you want to keep as favorites. Then you will be seeing the favorite heart on your keepers, when you view the Recently Deleted album and will be warned. Don't use mass delete. Empty the recently deleted album, as soon as it so full, that you cannot see all photos in it at a glance. This will work on all system versions.
On iOS 16.1 or later you can split your Photos Library into two separate libraries, if you are willing to invest into iCloud Photos. I am using the iCloud Shared Library only to share my library with myself. It is highly convenient. How to use iCloud Shared Photo Library - Apple Support
I now have to separate libraries on my iPad and iPhone, a personal library and a shared library and can toggle with on click to see the personal library or the shared library or both together.
- All new photos are arriving in the personal library. That is the working space, where I am sorting, tagging deleting photos.
- The important photos I want to keep or to show to other people will be moved to the shared library.
- When I delete photos, I switch to the personal library. Then it is impossible to select or see the photos in the Shared library, where my best photos are.
On an iPhone, that can be upgraded to iOS 18.4 you can use a different approach, without iCloud.
- Add all photos, that you do not want to delete to some album.
- Then use the filter to show only photos, that are not in an album, when you are about to delete photos.
You will find the filter option "not in an y album" in the tab with the two arrow (up and down) below the All Photos view, but only on system version 18.4 or later.
