iPhone X cellular signal dropping

hello,

I have an iPhone X with iOS 13.5.1, the cellular signal keeps dropping sometimes, then I have to enter Airplane mode and disable it again, and I got Signal, what helped to reduce the dropping is to turn Bluetooth off. It wouldn’t be that much of a Problem, if people were able to call me, mostly they got “user busy” or it just didn’t work. I don’t get incoming calls. When people call me, the celullar signal mostly is dropping to zero, sometimes it won’t.

IMEI is showing, so I don’t think that it is a baseband failure (could still be, but I hope not!)

The Antenna’s connected to the mainboard are all together right? Cellular, wifi and Bluetooth? or am I wrong?

I resetted the phone and the carrier settings and updated it, the carrier settings update worked a bit, so I got less droppings.

i have another iPhone X with the same carrier, I got the same signal on both of them, as it seems now, the signal is only dropping when i receive incoming calls (but it won’t show, because I have no signal when somebody calls me)

maybe somebody had the same problem or have an idea what it could be.

thanks

btw: as it seems, the wifi is also dropping sometimes, not to zero, but I don’t have a constant signal like with my other iPhone X.

so as it seems, it won’t find a 3G connection, 4G and 2G works, IMEI shows, but no 3G connection.