On Umbrel you can switch from Bitcoin Core to Bitcoin Knots without resynchronizing. All it takes is dragging your existing data folder into the Knots app. Here's a quick step-by-step walkthrough if it helps:

FYI: The replace popup only shows up in umbrelOS 1.4.1 beta 1. For now you can just: - Stop both apps - Go to Files > Apps > bitcoin-knots, and delete the "data" folder - Then go to Files > Apps > bitcoin, and cut/paste or drag-and-drop the "data" folder in Files > Apps > bitcoin-knots Works like a charm!