Schonbrunn Palace website offer a few tour ticket options. I mainly interested in a seeing the architecture and gardens and don’t want to join any paid tour if unnecessary. Is there a general ticket or free area to visit?
If I remember correctly most people take an audio guided tour. If you are going to travel out to there I would at least do a tour of the palace. Some of the grounds are free to enter.
The gardens and grounds are free with a few minor exceptions (labyrinth/maze and zoo).
The palace is reachable by subway from the center in 15 minutes.
Most tours are self guided with an audio guide available.
https://www.schoenbrunn.at/en/tickets-and-prices/all-tickets-tours