I never noticed a manual bitlocker lock option missing from the right-click menu, but wanted to add it. Found the below method, which works well:
https://www.tenforums.com/tutorials/374 ... -10-a.html
I use an internal drive for local Veeam backups to a bitlocker encrypted drive. I leave it locked whenever backups are not running, which keeps it more secure from ransomware, etc. I do not enable the auto-unlock option for the same reason. It's nice having the right-click option and I'm surprised this isn't a native feature.