The latency will only really be an issue for voice/video calls plus gaming, for streaming and web browsing in general its not noticeable.
You have to remember that 5g frequencies do not propagate as far as the lower 4g and 3g bands, so 5g coverage is generally always worse. It doesn't get better in as much as most 5g installs are NSA (Non-Stand-Alone) so are effectively 5g radios on a 4g base station.
As per Opti, if you have a cellular modem then consider an external antenna (keep the coax length as small as possible) as that will improve reception significantly and again, a directional antenna will be even better.
At least 1 mobile company are definitely using the older 900MHz and 1800MHz frequencies for 5G (NSA), which can manage good coverage (but obviously lack the bandwidth of the higher frequencies).
NSA (which all UK operators publicly use currently) obviously doesn't impact coverage, only bandwidth (and other features that aren't relevant to this discussion) is impacted compared to SA. I do sometimes get to play with SA when I CBA, and the speeds and latency are impressive (usually around 1Gbps down), obviously still not near fixed line capabilities, but I suspect once these cells fill up, and the cells start to breathe, speeds and coverage will suffer.