I read that page with interest, however was not surprised that it offers zero evidence to support it's claims.
In fact they completely discredit themselves in their first paragraph:
They clearly don't understand that 5G is a modulation mode, which can operate on any of the existing phone bands.
And of course they offer no evidence that modulation is relevant.
Secondly, the whole point of 5G is to replace the existing high-powered phone bases with multiple sources using much lower power.
So if anything 5G will dramatically reduce the average power levels.
It's pretty obvious that their push for a further study is a rather pointless scare campaign.
If they are so concerned, why don't they start a "fund-me" campaign and do their own study?
Designing a worthwhile study is surprisingly simple, and the equipment can be rented quite cheaply.
Whatever, there have already been a large number of independent and well funded studies, none of which have demonstrated a convincing correlation.