Here's my suggestions... Lot's of these will be off the beaten path, because the popular tourist areas are inundated with out-of-state tourists, so not only are they far more crowded than usual, the crowds showing up lack any sort of outdoors ethics.
Also, please try to be as self-sufficient as possible. Some rural towns are encouraging tourists to stay away this summer, because of concerns over medical system capacity. Bend and many coastal towns in particular.
Anyways, here's my list:
1) Start in Fields Oregon. This is small town population 7 (last I was there) but is the hometown to both Avlord Desert and Avlord Hot Springs. As long as there's no precipitation, you can camp out in the middle of playa. I think Larry had some pics up a little while ago.
2) From Avlord Desert, the next logical stop is Steens Mountain loop.
3) After looping the Steens, you can head north towards burns, and stay at Crystal Crane Hot Springs. They have reopened, and overnight guests get all-night pond access. https://www.cranehotsprings.com
4) From Burns, you can head west into Bend. However, the Hwy 20 drive here is about as boring as they get. I suggest instead to skirt slightly south, and drive through Christmas Valley and Fort Rock, and highly recommended stop at Crack In the Ground.
5) After Fort Rock, you can head NW towards Bend, but I'd suggest a stop at Paulina Lake. This is at the top of Newberry Caldera, with both Paulina and Twin Lakes up there. There's Hot Springs in the bank of Paulina Lake, with a nice hike though some obsidian flows. While at Paulina, you can ride the Paulina Plunge, which is a mellow downhill ride along a series of waterfalls and swimming holes. Because of shuttle logistics, you might want to consider doing this guided. Downhill Waterfall Mountain Bike Tour | The Paulina Plunge
This area has a ton of geologic features, including the Lava Cast Forest, Lava Butte, and numerous lava tube caves. High Dessert museum us nearby too.
6) From here, you're basically in Bend. The downtown river tube float is fun on a hot day. Restaurants have limited indoor service, but most have outdoor dining anyways. And of course, mountain biking. You could spend weeks here, and not ride every trail. My favorite option is shuttling up to Todd Lake, and riding the back country trail network through Tumulo Falls, and back to the Phil's trail network.
7) No trip to central Oregon is complete without exploring Cascade Lakes highway. Lots of camping, hiking, lakes, cross country biking etc.
8) To get away from crowds, I suggest heading south from here. You can stay on pavement to Cresecent cutoff, or take the dirt trails from Cultus Lake area to Waldo Lake. Good camping any of these areas. But keep going south until Highway 58. You have a short detour option here to ride at Oakridge. Willamette Pass is closed this summer. But then head slightly east on highway 58, and follow the signs to Crescent Lake. Then use the very primitive dirt road to get to Summit Lake. If Summit Lake is too crowded, take the even more primitive dirt road to Timpanogas Lake. There's a small campground here, and you can have the lake to yourself most of the time. https://goo.gl/maps/HLEc5uxYbJZb6Z147
But the real gem is a short hike or bike ride up to Indigo Lake. This should not be missed! https://goo.gl/maps/teVtQAdNAoT8YYm38
9) From here, you can head south again to Lemola Lake. Not much special here (but still nice), but the main reason is to ride Umpqua River Trail, from Lemola Lake to Umpqua Hot Springs. This is a shuttle ride, but depending when you're there, I'd be more than happy to join you guys and help with shuttle. It's one of my favorites.
This puts you next to Highway 138, where you can follow vandiesel's route to the coast. But... my next suggest is to bail from the coast at Newport, and coming into Corvallis.
10) Just south of Corvallis is Alsea Falls rec area. This has become a well-developed MTB area. It's all out and back, no shuttle needed.
11) After Corvallis, stop by Falls City, for even more out-and-back riding.
12) After Falls City, there some nice riding at Silver Falls State Park. I also recommend doing the main waterfall loop hike.
13) From here, might as well stop in Portland. Despite what Fox news portrays, the city is most definitely not burning to ground, although the PDX areas is still on tight Covid restrictions, so dining out is limited (plenty of take out and food carts still!).
One neat option to spend a day in town is doing the 4T trail. https://www.travelportland.com/culture/4t-trail/
14) This pretty much brings you to Gresham, but after Gresham, a day or 2 riding Post Canyon in Hood River is definitely worth a stop.
15) My last can't miss recommendation is stay a night or 2 at Wallowa Lake State Park on your way home. This is another of my favorite areas.