I simply open the app, create a network, enter the network ID, but when I try to move the slider to the right to enable the connection, I just can’t. It won’t stick to the right, it comes right back to the disabled position. At the bottom, I see “Node address not set OFFLINE”.
My network does work: I have two computers in it, and they see each other.
Got it working now. It was a problem with the VPN I use. Since I also use it in Windows and Linux with ZeroTier without any problems, I thought Android wouldn’t have a problem with it, either. But it’s not the case, apparently Android cannot handle two VPN services at once. So I disabled the other VPN, I disabled the “Always on” option, and now it works.
FWIW putting ZeroTier in the split tunneling options of the VPN didn’t work.