I was able to do some research and according to the manufacturer, the router has only been successfully tested with Huawei modems, so they are compatible according to the manufacturer. Otherwise you would have to test whether it could also work with a Nokia modem, but there is no information here and unfortunately I cannot confirm this.

It's easy to do, I was in a hurry and used the web method (https://forum.openwrt.org/t...), it took less than 10 minutes and the thing was flashed. I've owned and used it for almost 3 months without any issues. The only downside is the hideous frontal LEDs can't be controlled/deactivated via this image, so I put a piece of masking tape on it.

However, the router does not have a SIM card slot and therefore cannot be connected directly to a 4G or 5G network. However, it does offer a function called tethering, which allows the router to be used as a 4G or 5G router replacement.