It still has a big indirect impact. People are less likely to vote if they feel like their vote doesn’t matter as much, and someone in a heavily gerrymandered state does in fact have their vote matter less, at least locally. Turnout would probably be measurably higher if the districts were fair or competitive.

There are other indirect effects too - there are plenty of states where Republicans are only able to pass voter-suppressing policies because of the legislative edge they hold thanks to gerrymandering.