The rule of thumb: if you set your device with correct antenna gain (which, AFAIK, is already hard coded in models with fixed antenna) and select correct country, then you're completely safe. Country regulations limit EIRP to a safe number ... EIRP stands for Effective Isotropic Radiated Power and number represents power level, present in direction of highest power with directional antennae. Most countries limit EIRP to 30dBm, which would be 1W of power radiated to whole space. With directional antennae signal level in "main direction" is the same, but it's much lower in other directions. And according to most (all scientifically relevant) studies, this signal level is not harmful to human beings even if exposed for prolonged periods of time.

With broadband the reasoning is a bit different because country limitations are not set as rigid. There rule of thumb is that Tx power for terminals is limited to something like 200mW, which translates to 23dBm. Add antenna gain (e.g. 17dBi) and one gets EIRP of 40dBm. Which is not really excessive but not small either. The good news is that Tx power of terminal is highly regulated by cell tower and if signal level from cell tower is decently high (e.g. RSRP is better than -100dBm), then actual Tx power from terminal will be lower than maximum - cell towers want to have all signals from all connected terminals at around same level, hence closer terminals will have their Tx power reduced. Reduction in Tx power is often in range between 10dB and 20dB, making EIRP between 20dBm and 30dBm.

Power radiated in other directions is much lower, with high-gain antennae the difference between "main direction" and the rest is actually even higher than with more omnidirectional antennae. LHGG LTE6 has 17dBi antenna, which means that power level in other directions are likely 30dB lower - that translates to 1000 times lower signal strength (the ratio may be actually even higher).
Brick wall quite probably attenuates signal by some 20dB, making signal from your LHGG 100.000 times lower than radiated in main direction. If you have your mobile placed near the bed during night, you're probably getting similar amount of energy from that source (because mobiles use omnidirectional antennae, even idle communicate with cell towers from time to time and probably enables WiFi periodically to maintain wireless connectivity).