Idaho is very nice, around Stanley are the Sawtooth mountains but there are many places to visit. We followed 95 all the way north to Bonner's Ferry last year. Then turned east on Hwy 2 to kalispel and Glacier.
Minnesota/Wisconsin are on our list but we avoided it this year because of the governors. Hopefully that will be resolved next year. But you have to time a visit to avoid the Black Flies in early summer.
The PNW is another possibility, also an area that with have recovered from the mass hysteria by then. Oregon, Washington and Northern Cali. Lots of great scenery.
New England was a one time trip for us so the kids could say they've been to all 48 states, Mexico and Canada. And for the US History. It is packed with people. The southern end is hotter than Hades. Maine is nice and if Canada is reopened you can from into New Brunswick there. Acadia is an odd park, bits scattered all over a large area. NH, VT and that park of upstate NY all have good camping