I got the exact same experience. Around 5-7mbit/s download with RUT240 while 85mbit/a with iPhone XR. I also have Telia as operator, located in Sweden, on both SIM. I called Telia yesterday and they didn’t not find any issues on their side. For unknown reason they will send me a new SIM card to try with. I haven’t received it yet so I will have to come back with results.
I will also try with another router today, using the same SIM, to verify if the network speed is as poor as with the RUT240.