A good first place to look is Window > Devices & Simulators in xCode, then find the details for your device. There may be error information here that helps you find the fault.
Restarting devices and installing updates seem to fix this problem for a lot of people.
For me, there was a red notice in the device window about connection to the device and it turned out to be the cable that was at fault.
This was an official Apple cable, just a few months old, and still works fine for charging and data transfer; and I've been using it with xCode without problems for a couple of months. It seems to be possible for Apple cables to develop some tiny physical fault that seemingly only xCode is sensitive to.
Using a different cable worked first time for me.
There seem to be a few variations on the exact error message with the same root causes varying depending on exactly what xCode was trying to do at the exact moment it failed: I'm on xCode 12 and for me it was:
Failed to start remote service on device
Failed to start remote service com.apple.installation_proxy on device