I also experienced a DNS-related issue when using ssh to connect to my work remote server, both on BigSur 11.3.1, and even now after an update to 11.4. In my case the issue manifests with an ssh connection hanging for an infinite amount of time on my mac, while it works flawlessly when using other computers (also when connected to the same wifi network as my mac). Strangely, despite the ssh connection doesn't work, pinging or browsing the web pages hosted under the same server do. Eventually I had to use a workaround solution, which was to do ssh using the IP of the target server instead of the domain name.