That doesn’t sound legal to me unless you’re taking weeks off and claiming sick time. I do know that you get up to 40 hours of paid sick time legally after working some amount of time over the year and for a time (but I think no longer) COVID was a separate paid sick time thing.

If you really got fired over sick time I’d consult a an employment lawyer. Good to grounds for a lawsuit and re-instatement but I obviously don’t know all your details