CA-47, MI-07/8, MD-06, VA-07
These are 5 seats that would be close to likely D if the Dem incumbents ran, but are now tossup due to being open seats. CA-47 is well Orange County, and Republicans have managed to recover significantly since 2018. The Michigan two are obvious. MD-06 will go comfortably for Biden, but Hogan will likely carry it by double digits. Whether the house race tracks closer to the Presidential or Senate will be key. VA-07 will vote Biden again, but it's unclear whether Trump does worse in VA this time around. Additionally, the GOP is likely going to nominate a better candidate than Vega.
I can see one of the Michigan seats flipping, but doubt the other ones (especially MD-06 and VA-07) do in a presidential year.