I got one in January and didn't need a return flight as its a 1 year visa. If you plan it right, now the borders are open again, you can leave & return to Thailand within the date of your visa - and get a 2nd year stamp 😊
For OA visa, if you exit & re-enter Thailand before the end of your visa dates, then you will get a 2nd year stamped in - ensure you have insurance for that year