I've just recently added a 2nd monitor. Until now, I've used 9 spaces, set so macOS does not rearrange them. I use Command-X (where X is from 1 to 9) to move to a particular space. I also use Command- to move left and right between spaces. Same with sideways or vertical 3 finger swipes. (I have it set so it behaves as if my spaces are in a 3x3 grid.) The left and right movements are set through the macOS Settings and the same with the number keys taking me to a space. The others are programmed through BTT. If needed, I can always bypass what I've done in Settings and use BTT to define the key actions.
This is a big part of my work habits and I use different spaces for different tasks. I'm running into problems with a 2nd monitor. There are a number of reasons why one monitor may be off, temporarily. When that happens, macOS shoves all my windows back onto the one monitor that's on. Even if the other monitor is off for only 1-2 seconds, the windows do not go back to their previous positions on both screens.
I know I can use "Displays have separate spaces," but that creates other problems. I found when the pointer is on one display and I move to a new space, the other monitor space does not change.
Is there a way to use BTT to change the space on BOTH monitor screens at the same time, so I can make my gestures and keyboard commands to move both spaces at once? Or some way to have one screen follow the other if it moves?