Than what?
>RF can raise body temperature slightly at high enough powers
Undetectable tissue heating; the difference you experience from going outdoors from indoors is many, many times greater than what you mentioned.
>(any one who has been in an MRI for a while knows this, though that is much higher than 5G)
Then why even bring it up? You mention at the end of your reply that you're not trying to fear monger.
>This is a high-frequency signal
But lower than the visible spectrum and ionizing radiation.
>Maybe it's like so many other things: fine in small to moderate doses, but harmful in large ones?
Mate, you're being bombarded by electromagnetic radiation every second of your life, in quantities which eclipse anything you mentioned.
>but the bottom line is we don't know
Yeah, "we" do; folks much brighter than I have spent a really long time studying this stuff and their findings are available for consumption by anyone interested to learn more.