Some scientists were completely and demonstrably wrong on Covid.
Prof John Ioannidis of Stanford is an obvious one. He argued that governments were overreacting to Covid and predicted that deaths is the US would not exceed 10,000 - a figure that ultimately was less than 1% of the total deaths in the US.
I expect, though, that you are referring to anyone who predicted a greater number of deaths than ultimately occurred.
Arguments like that usually misunderstand what the science was.
For one thing, Covid 19 was a new virus and, although scientists could refer to similar viruses to extrapolate how it might evolve, it is not something that could be predicted with certainty. Scientists could also not predict what measures governments would introduce to limit the spread.
Accordingly, predictions had to be made with references to variables. I.e., what would a best case scenario look like (Covid quickly evolving to become less lethal, strong measures in place to prevent the spread) versus a worst case scenario (Covid evolves to become more lethal, and no serious measures are put in place).
Of course, Covid did become less lethal over time (which was always viewed as the most likely scenario) vaccines were created, and most countries introduced strong measures to prevent its spread.
Just because the worst case scenario doesn’t come to pass every time (particularly when active steps are taken to prevent the worst case occurring) doesn’t mean the science was wrong. If a better outcome than the best case scenario, or a worse outcome than the worst case scenario occurs, then it’s reasonable to ask what went wrong - but neither of those things happened.
(I imagine there are several scientists like professor Ioannidis that were completely and demonstrably wrong, but that does not equate to ‘all of the science being completely wrong’.)