Developer Mode Apple watch disabled

Hi to all,

I'm new to WatchOS development and trying to install the default Xcode 'Hello World' app on my Apple Watch Ultra. I've enabled Developer Mode on my iPhone and did the same on my Apple Watch. After enabling Developer Mode on the watch it asks me to restart the watch. After a restart it asks me again if I want to enable Developer Mode. Of course! I don't succeed in installing the app on my watch because Xcode is "waiting for first unlock" of my watch. When I look in Settings > Privacy > Developer Mode the toggle switch is disabled. I can enable the switch but the watch asks me to restart and this is the loop I'm in.

Anybody suggestions for 'permanently enabling' Developer Mode on my Apple Watch?

Thanks in advance!