Well, some died, like Michael Antonelli and Cristopher Marsilla.
It didn't seem like a great year for Gaviria or Sagan, nor Matthews who had to withdraw from the 2020 Giro after catching it. I don't recall if others had to do similar in 2021. All three of them dropped down the UCI rankings.
Curiously, almost as many riders seem to be blaming vaccination side-effects (Fuglsang and Van Avermaet among them) as covid infection for their loss of form, at least in public.
Really, the best covid-related excuse would have been Elise Chabbey, who was working as a front line doctor during covid, but she had a pretty good year, ranking 19th in the Women's World Tour, although with the only win being the Tour of Britain's mountain classification.