I have the same issue with iPhone XS 14.6 , it worked fine on IOS 14.6 for some time but as of last 2 days , i have no signal whatsoever on my primary (physical sim). However on my eSim with different carrier , it works fine.
The physical sim works fine on an android device.
On the physical sim majority of the time its either searching or "no service"
and say 1% of the time i get the carrier name showing up with no bar , but would go back to "no service" again