5G rollout is in its very early phases and teh most common band used at the moment is n78 (3500MHz) which does not have great in builidng penetration. Once n5 (850MHz) is repurposed from the 3G service over the next few years, then in-builiding speeds will increase on 5G.
If you are wanting reliable, high speed internet inside, then 4G is still king for the time being (unfortunately, your modem probably isn't 4GX compatible either).
Never be afraid to back yourself when trying new things, just always make sure you have 3 escape routes if things go wrong.
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