Is 32GB of RAM at 3600MHz plug-and-play, or does it require tweaking?

It’s not exactly plug-and-play. Running two 16GB dual-rank sticks at 3600MHz stresses your CPU’s memory controller more than two 8GB sticks, especially on Ryzen. You might need to check your motherboard’s QVL, manually set voltage, or loosen timings. Most people with a well-binned kit from G.Skill, Crucial, or Corsair on a modern platform (Ryzen 5000/7000, Intel 12th/13th gen) have no issues, but it’s more common than with 16GB kits.