Check the trash folders before you try anything else.

1. Google Photos: open the app, tap Library > Bin (or Trash). Items stay there for 60 days if they were backed up, or 30 days if not.
2. Samsung Gallery: open Gallery, tap the menu (three lines) > Recycle bin. Photos stay about 30 days.
3. Other gallery apps have their own trash. Look in the app menu.
4. Cloud backups: check OneDrive, Dropbox or Samsung Cloud if you ever turned them on.

If the photos are not in any trash, recovery apps for Android exist, but results are poor on modern phones with encrypted storage. Do not install many apps or take lots of new photos, because new data overwrites the free space.

Turn on Google Photos backup afterwards so that this does not happen again.