Thanks for the bug report, Peter.
I have confirmed your issue and have added a ticket here:
https://buddypress.trac.wordpress.org/ticket/4999
The ticket has a patch that will add back the “Forums” tab so you can configure the old legacy forums.
Moving forward, the legacy forums will not be the preferred option and you should look to use the bbPress plugin.
Check out this codex article for more info:
https://codex.buddypress.org/user/setting-up-a-new-installation/installing-group-and-sitewide-forums/using-bbpress-2-2-with-buddypress/
