some are in safe districts for their party...it will be interesting to see what happens in the GOP primaries with pro-Trump vs. anti-Trump candidates, and the eventual winners' chances against Dems...mostly in the House races...for the Dems retiring, most of the CA and NY seats won't be a problem...nonetheless, the Dems need to be very active...I suspect they will be.
As for the Senate, PA, OH and NC could be real challenges for the GOP...don't know much about Leahy in Vermont, but would be surprised at loss there for the Dems.
Link: https://ballotpedia.org/List_of_U.S._Congress_incumbents_who_are_not_running_for_re-election_in_2022