Impeachment can also be for egregious misconduct that isn't specifically a crime. It's similar to the "unlawful v. illegal" distinction, the distinction in this case being that Impeachment is reserved also for "High Crimes", ie Crimes that most citizens wouldn't even be capable of committing, because they are only possible when holding High Office. I suppose an absurd example would be trying to start a war without support of Congress.
More mundane crimes that Trump is (likely) guilty of include tax fraud, election law violations in various States such as Georgia; you could probably add sexual assault to the mix as well. Many of these haven't really been pursued in the last few years, at least beyond attempts to gather evidence, because as President Trump has enjoyed virtual immunity from criminal prosecution.