In theory, it could've been worse for the GOP. If there's any solace for the GOP, it's that Newsom hasn't gained from Biden. Still, no one can deny that this was a heavily disappointing result for the GOP. Period, end of story.
Seems as like for 2022, California Republicans probably shouldn't be worried much about trying to make inroads in many places so much as they should be worried about trying to retain what they already have.
To be fair, there are some seats like CA-10 and maybe CA-45 and CA-49 where if Republicans had put up a strong candidate and campaign in 2020 that could have flipped it. Of course redistricting will change what these seats look like but generally a Biden single digits seat is winnable for them even if they didn't seize the opportunity in 2020.
We do need to wait for the full results to see how Newsom did in the swing districts, and it may be that stuff like this intensifies bad trends for Republicans and reduces split-ticket voting.