Today, I don't see the Democrats losing big. I say the Democrats gain a couple of seats in the senate, perhaps 3. The house is quite another matter. But losing 13 seats in 2020 may not have been a bad thing. That leaves the Democrats with less seats to defend in 2022. Instead of 235 seats, they now have 220 with 2 seats vacant which will be filled in a special elections come Nov.
Without redistricting being completed, it's hard getting a feel of safe vs. competitive districts or districts which could switch or change parties. Perhaps looking at the past first midterm elections when a president either made independents angry or not, plus job approval from independents.
2018 Independents angry at Trump, 35% approval, GOP lost 44 seats and control of the house
2010 Independents angry at Obama, 41% approval, Democrats lost 63 seats and control of the house
2002 Independents happy with Bush Jr.,59% approval, Republicans gained 8 seats, retained control of the house.
1994 Independents angry at Bill Clinton,40% approval, Democrats lost 54 seats and control of the house.
1990 Independents happy with Bush Sr., 53% approval, But the republicans still lost 7 seats.
1982 Independents angry at Reagan, 40% approval, Republicans lost 26 seats
1978 Independents angry at Carter, 42% approval, Democrats lost 15 seats
Keep in mind, the approval rating is from independents and independents only, not all adults. Also the approval rating is nationwide, not district by district. Also during Carter and Reagan independents made up only around 25% of the electorate, so their impact would be less than it is today with independents put at 40% plus.
Also, independents are happy with Biden as of today with 51% approval. Which would put the upcoming midterms more in line with 1990 and 2002 for the party in power than any of the rest.
One last thing, Gallup puts party affiliation at 30% Democrat, 24% Republican, 44% independent. But if you count independent leaners you end up with 50% democrats/independents lean Democratic vs. 41% Republican/independents lean Republican. As of 18 Jun 2021 that is.
Conclusion, as of today, the Democrats are in good shape to retain both chambers. But no predictions or forecasts except for the senate.