From what I've heard, the more "popular" public parks near the Denver Metro (ie within 2 hours) here in CO are definitely crowded on weekend... very hard to get a reservation unless you find someone who cancelled. They also leave reserved spots empty, even if the person with the reservation doesn't show up. Some that have good cell service are even full on weekdays because so many people are working remotely, so as long as they have phone service, they can work. But, if you are a little further away from Denver Metro, you likely will have better luck.
I was up in Medicine Bow National Forest last weekend (in Southern WY between Centennial and Saratoga), and while we weren't camping, I checked out nearly every campground out there. Every single one was full, all are first come. Normally these sites aren't like that... they get mostly full but not totally full, with tons of people boondocking around too. That's a good indicator of how it's been this year. After Labor Day may be better but then it starts to get pretty cold.