Hello,
To start with mobile connection, your received mobile signal strength indeed seems to be very weak, especially RSRP value, which is in range of no connection at all. Just in case you would like some reference values, they can be found here. Is it possible that during SIM change something happened to device, which is causing these new issues? For example, is it possible that mobile antennas was removed for convenience to access SIM slots and not connected fully afterwards? Or if wired antennas are used, maybe they were moved slightly and placed in worse location near before, e.g. near any object which can block or interfere with signal?
There is also a possibility that something had changed from mobile operator's side and that this issue is not related with router itself (especially that issue happened with new, which can indeed be related with internal operator's changes)
Despite the signal which your router receives, it seems that it should have internet connection, at least ICMP pings indicate this. Is it possible that your computer no longer has DNS servers configured on it? That would explain why ICMP pings are successfully, but you are not able to browse the internet. Try to open computer's network settings, especially if you are using Static IP address, try to set DNS servers to "8.8.8.8" and then check if that allows computer to browse internet.
It might also be beneficial for testing purposes to try connecting another device to the router, e.g. mobile phone via WiFi. If you would connect new device via WiFi to the router, does that device acquire internet connection from the router?
