I'm not aware of any evidence that 5G (of either the cell phone or WiFi type) causes COVID-19, nor any reason to think it could. But there are a bunch of people with serious scientific and engineering qualifications who assert that there is evidence for wireless signals damaging human health. This needs considering:
https://www.5gspaceappeal.org/the-appeal
Some other people will academic qualifications who have spoken publicly about their concerns about 5G radiation;
* Professor Dariusz Leszczynski (PhD, DSc)
https://researchportal.helsinki.fi/en/persons/dariusz-leszczynski
* Dr Mary Redmayne (PhD)
https://research.monash.edu/en/persons/mary-redmayne
Of course that doesn't means they're right. It just means the evidence they discuss is more likely to be worth checking out than blogs by random cranks on the net, like me ;)
Just to give you an idea of how "precautionary approach" is supposed to operate - imagine someone raises a "valid concern" like this:
Is there evidence of safety of Mastodon and other federated social networks? If there's no evidence of safety, we shouldn't probably be using them, because they could be potentially unsafe. For example, there might be an increased suicide rate associated with use of federated social networks, and nobody has proven that there isn't.
