Slow Home Internet

The 4G LTE signals, in theory, can cover many miles but as you get farther away from the tower the speed drops off. The 5G NR channels can reach out but the n41 does not reach out as far as the n71 signals as the wave lengths are not the same. The n41 is a higher frequency than the n71 and the n41 does not have the penetration that the longer n71 has. 

You provided this as signal data:

Primary (B66):  RSRP: -106 dBm, SNR: 13 dB, RSRQ: -11 dB.

Secondary (n71):  RSRP: -112 dBm, SNR: -1 dB, RSRQ: -14.

So, we know it is a n71 5G NR signal on the secondary and 4G LTE on the primary signaling. We can also tell the signal strength on either is NOT stellar. If the SNR on the n71 is as stated that is very poor signal to noise ratio. The combination of barely fair signal and poor SNR does not fare well. It is not promising. If the tower is line of sight and no obstructions an external antenna could help some but I am not sure if it would be sufficient to compensate for the weak signals. It looks to me as if the tower is just too far away for a solid signal. Tower location and distance to the tower is important.