Seems odd that the macOS Desktop app would have an option to delete your account, as this option is normally available only in the Web Vault (in the “Danger Zone” area):
On the other hand, I don’t use Bitwarden on macOS, so I could be wrong.
If you don’t find a “Log out” option in the menus, have you tried opening the Account Switcher in the upper left corner of the UI (to the right of the Search bar)?
Your other option is to Lock the account, because there is a Logout button next to the Unlock button on the unlock screen:
