How to turn off the Bell sound in Windows Terminal: (Based on this post on the Windows Commandline Dev Blog)
Open Settings and under each profile you want to disable the bell for add "bellstyle": "none"
Not much else to say about it really, I use tab completion a lot in the terminal and it beeps at me every time so I wanted to turn it off. There's an old (and closed) StackOverflow question about it here but all the responses involve customising your bashrc or equivalent.