I was recently made aware you should be able to use Powertoys (as maybe the only way) to remove the innate win+space shortcut and override it with e.g. your launcher.

This works... it shows the launcher. But I still find myself with the wrong language selected every couple days, I have a feeling it does not fully work when I use win+space inside an RDP connection or.. somewhere else.

Mildly infuriating if you can't just disable OS-level shortcuts.