How do I delete unwanted albums in the Mac Photos app?
Select the Album, hit the Delete / Backspace ⌫ Key, or right / control click on it and select "Delete Album"; click on the "Delete" button that appears on the confirmation dialog at the top of the app (Are you sure you want to delete this album?).
I find a same post in this forum and the answer to your question, you can check it. Delete album from Photos.app