You can install faster RAM — it will just downclock.

Yes, it will work, but the system will run all RAM at the speed of the slowest stick, which in this case is the soldered 3200MHz.

That 3600MHz kit will clock down to 3200MHz automatically. It might even run at a slower speed if the system can’t find compatible timings, but usually it’ll match the soldered stick’s JEDEC profile. You won’t get the extra speed, and you’re paying for something you can’t use.

Dual-channel mode still works fine if the capacities match well enough, but the speed ceiling is set by what’s soldered. There’s no trick to bypass it.

If you’re buying RAM for a soldered system, save the money and get the same speed as the soldered RAM.