You can disagree with him on the science if you want... but it's unfair to call him a "grifter". He's also not the only person saying this kind of stuff. Check out this article in Nature basically saying the same stuff he's saying:
Five reasons why COVID herd immunity is probably impossible
There’s another problem to contend with as immunity grows in a population, Ferrari says. Higher rates of immunity can create selective pressure, which would favour variants that are able to infect people who have been immunized. Vaccinating quickly and thoroughly can prevent a new variant from gaining a foothold. But again, the unevenness of vaccine roll-outs creates a challenge, Ferrari says. “You’ve got a fair bit of immunity, but you still have a fair bit of disease, and you’re stuck in the middle.” Vaccines will almost inevitably create new evolutionary pressures that produce variants, which is a good reason to build infrastructure and processes to monitor for them, he adds.
So nature is also saying the same thing... mainly that vaccines will not result in herd immunity, and that the vaccines will put pressure on the virus to mutate to become vaccine resistant. Is Nature also a grifter publication? They're essentially saying the same thing as Geert, just a few weeks later.