In most cases (those being where the actual occurrence of a Covid infection was verified by a positive test), the causal basis for attributing long Covid symptoms to Covid infection is the same as the causal basis for attributing vaccine injury symptoms to vaccination.

It's good to question what other factors might alternatively explain illnesses, but double standards don't help. I don't see any useful difference between "you call it long Covid but it might have been an environmental toxin or something else" and "you call it vaccine injury but it might have been an environmental toxin or something else."