After using countless flashes on my Leica M and Leica Q series cameras, I found that the best option is still the Leica SF40 for on camera flash. It’s lightweight and mostly accurate in TTL mode. For off-camera I use the Profoto Connect Pro for Leica with the Profoto A10 or Profoto A2. I selected the A10 for Nikon because the flash works perfectly on camera if needed in manual mode. I have tried the Godox Leica triggers with little success of accuracy in TTL mode.
Leica SF40 Flash https://amzn.to/4fV2cTW
Profoto Connect Pro Leica https://amzn.to/3Cy4ZUC
Profoto A10 Nikon https://amzn.to/3V04Mjg