How do I delete photos on my iPhone12 when the trash icon does not work? When I sync with a MAC, it starts to add more pictures back on my iPhone and I cannot delete it. Running out of storage on my iPhone.

Synced photos from a computer can only be removed the same way they were put on, that is by removing them or deselecting them in the Photos section in iTunes or Finder depending on version of macOS you Mac is running and syncing again.

If you need to delete the photos from the iPhone, disable "Sync Photos" or if you have "Selected Albums" turned on, then deselect albums that you no longer want to sync.

You cannot delete synced photos directly on the iPhone at all. Synced photos are stored differently from the photos you are saving to Photos. You have to sync again, but select less photos. Omit all photos you want to delete from the new sync. Do not enable “All AlbumS” but “Selected Albums”, and select none.

It won't allow deleting them on the iPhone No,. It will in and of itself remove them on the next sync.

If you turn off Syncing photos and sync again, it will remove all synced phots thus deleting them from the iPhone.

If you select different albums to sync, then to will sync those instead and remove photos that were in the deselected albums.