For the BTT Mobile app, the idea here is to connect a bluetooth keyboard to the iOS device and have the app forward the keyboard's unmodified keystrokes directly to macOS, so that BTT or similar software such as KeyKarabiner can process the inputs directly.
The goal is to use this in tandem with a remote desktop viewing app, so that you can still access all of your BTT keyboard shortcuts while working via remote desktop. Sending keyboard input through a regular Remote Desktop app (such as Chrome's) modifies the keyboard input in ways that make BTT ignore them (for example, holding modifiers or remapping hardware keys such as caps lock or function keys).
(Apple's Multi Peer Connectivity Framework seems to be for local connection only so this might be impossible, but I've long dreamed of having full BTT control while remote-desktoping so thought I toss the idea out!)