Fritzbox internet

FritzBox speeds

So i want to install a wifi network in our vacation home because there is not a single provider that can deliver internet to our location apparently. So we tried Tadaam for a while, but the speeds compared with pricing are not ideal. So i thought to buy a FritzBox (6850 LTE) and put in a SIM card. When it came in the mail, i tried wifi speeds on this thing with my regular sim-card from my phone. My phone gets 5G speeds up to 131Mbps, while the same phone connected to the FrizBox (with the same sim-card) only gets 30Mbps. Does anyone know what i am doing wrong? Is it capped because they want you to purchase a much more expensive data-sim? Is it because the FritzBox does not support 5G? This would really help me out.