Blueberries turning brown
It's a definite possibility that the symptoms you are describing are the result of heat damage. In situations where the heat increases very rapidly (like when it suddenly follows cool weather), heat damage can be especially bad. Researchers with OSU have actually been doing a lot of work in the past 5 or so years looking at this exact issue.
The bad news is that heat events extreme enough to cause damage to fruit impact immature fruit as well - you can kind of see that in your photo, where the pink fruit are slightly shriveled (or appear to be so).
Another possibility is that your fruit are infected with spotted wing drosophila (SWD), a very annoying pest that lays eggs in blueberries and other soft fruit. That's something you can easily check out. Here's a guide to a quick way to see if SWD larvae are infesting your fruit: https://catalog.extension.oregonstate.edu/em9097/html
If you're extra curious about SWD, OSU has some fantastic resources: https://extension.oregonstate.edu/collection/spotted-wing-drosophila-swd
If you have further questions, feel free to reply to this thread, or contact your local Extension office.