Pathfinder Rulebook, Starfinder Roleplaying Game Subscriber
Building a character and was wondering if I could have a cleric pick up a pantheon via the Syncretism feat or if they are too unlike deities to be chosen that way.
A pantheon looks mechanically similar enough to a deity that I don't see any reason why it couldn't be done. Whether it is allowed at your table is something that will have to be decided at that table though.
Since a Pantheon grants both a favored weapon and divine domains (the prerequisites in order for the Syncretism feat to offer any mechanical benefits), I would allow it. It's up to you to offer an interesting in-game explanation for your choice, though!