From WIkipedia:
John Lorimer Campbell is an English
YouTuber and retired nurse educator known for his videos about the
COVID-19 pandemic. Initially, the videos received praise, but they later diverged into
COVID-19 misinformation.
[2][3] He has been criticised for suggesting COVID-19 deaths have been over-counted,
[4] repeating false claims about the use of
ivermectin as a COVID-19 treatment, and providing misleading commentary
about the safety of COVID-19 vaccines.
[5]
Just to be clear, he's not a medical doctor - the "Dr." bit is from a Phd he did on teaching via digital media (university of Bolton).. He was for many years a nurse practitioner and taught nursing. Recently, one of his videos claiming that there were more excess deaths amongst folk who'd been vaccinated against COVID-19 was debunked on "More or Less" (the opposite was true) and after contact from the BBC, he withdrew it, stating that he wasn't a statistician... which begs the question why he was making such claims (based on statistics) when he knew there was a good chance he was wrong? Other claims he made in early 2024 about blood clots in cadavers were also debunked.
There's a lot more - a long history of false claims - but mostly he seems to peddle conspiracy theories to those susceptible to selection bias and who aren't capable of thinking (specifically, thinking critically) for themselves.
Personally, I feel it's both dishonest & intentionally misleading to use the title "Dr." when commenting in a medical context when you don't have the relevant medical qualifications - you should postfix your name with "Phd". Even with the postfix, it would still be more honest to make it clear what your qualifications actually are, especially if your doctorate was non-medical, e.g. in this case, digital media-related.