Why Leapdeck exists
macOS moves between Spaces one at a time. Control and an arrow key walk you through every Space between where you are and where you want to be. Mission Control is the other route, and it is a detour with a click at the end of it.
Full screen apps are the worst case, because each one occupies a Space of its own. The app you want is somewhere along a row you have to travel.
One key, and the Mac is already there
Leapdeck binds a hotkey to a Space and goes straight there. Nothing slides past on the way, and a full screen app is reached exactly like a desktop.
The hotkey follows the app rather than the slot. Give Xcode Option 2 and it stays Option 2 after you drag your Spaces into a different order. A shortcut bound to a position breaks the moment the row changes.
System Integrity Protection stays on
The usual advice for this problem is to disable part of SIP so a tool can inject into the Dock. Leapdeck does not ask for that.
The Dock does have to perform the switch, or Mission Control and swipe navigation end up pointing at the wrong Space. Injection is not the only way to ask it to. Mission Control's Spaces Bar is an ordinary Accessibility interface with one button per Space, and pressing one makes the Dock switch by itself.
That deserves to be put precisely. Tools like yabai inject for good reasons: creating Spaces, reordering them and moving windows between them genuinely need it. Going to a Space does not.
What it is not
Leapdeck does not create Spaces, reorder them, or move windows between them. It goes to the one you want, and that is the whole of it.
There is no account and no server. Which Spaces you have, and what is on them, stay on your Mac.