This problem has been bothering me on my corporate MacBook Pro since I got it. As people in this thread, I've been frequently rebooting to temporarily fix the problem. Today, after upgrading to macOS 12, the problem started occurring almost instantly after logging in. E.g. I could search for something in Google, only to find that DNS resolution was already broken when trying to open one of the results. I then remembered something they taught us 20 years ago, during our training for first line support for the largest Belgian ISP: remove the network adapter in device manager, then reboot and reinstall the driver. This was obviously a solution for Windows problems, but I figured it couldn't hurt to try doing something similar on macOS. So I went to the Network settings, removed the Wi-Fi service, rebooted, and afterwards created a new Wi-Fi service. I have about 4h of uptime since then, and DNS resolution is still working. Too soon to tell if it really fixed the longstanding issue, but going from breaking in just minutes to have working DNS resolution for hours definitely looks promising.