Uninstalling Exchange 2016 should be a straight forward process but sometimes you run into issues such as the one below:

The error is a bit misleading as it goes on to say that “Access is Denied”, however another server I was working on uninstalled just fine.
I rebooted the server and once I logged in again, I used the command line to uninstall but this gave me the same error:
"setup.exe /Mode:uninstall"
I gave it 15 minutes, re-ran the command, and this time, instead of staying at 33% on the Languages step, it went from 33% to 66% and then finished the rest of the uninstall.
DC Health was fine, no replication errors, my guess is that this server just took a bit of time to uninstall for whatever reason.
If you get stuck on this step, reboot the server, wait a bit and then try the uninstall again.
Hope it helps.