Trump endorsed candidates went 174 and 9 in the polls. That's not exactly a repudiation of Trump. Republicans outpolled Dems by 6 million votes. Redistricting, failing to work the mail in/early voting, and McConnell stiffing certain senate candidates with PAC money caused the lack of performance.
But the predictions for the Senate were way out of line anyway. 20 republican seats were up for grabs compared to just 14 Dem seats. And the prediction was to show a net 4 to 6 seat gain? No chance. But 2024 will be different. 20 Dem seats up for grabs while just 13 republican seats.