Used to be my stomping grounds, right up there with GNP and the Tetons for most jaw dropping views you'll ever see.
Hiking will be limited in the North Cascades then, but the drive over 20 from Mazama to Darrington is epic. Stop at the Diablo overlook for your mandatory photo session. One of thy least visited parks, so even "peak" times later in the summer are pretty low key compared to Yellowstone or Glacier. A couple of the main spots like Maple Loop Pass, Sahale Arm etc will always be busy but they comprise such tiny corners of the park
The Olympics will be in fine form by then and have some great valley hiking from Sol Duc side or Enchanted Valley. Of course hit Ruby, Rialto, etc. beaches. That time of year if you like to fish id book a half day with a guide out of forks and bonk some springers for the grill. My buddy guides out that way and is a good resource, also had some great airbnbs to stay at right on the river, close to the Hoh river entrance which will hopefully be back in action from last winters washout.