Allow me, a few weeks later, to answer my own question because the answers here are somewhat incomplete or misleading.
Actually, while Enchanced Dictation has indeed been removed from Big Sur (and Dragon Dictate doesn't appear to work on the combination of Big Sur and M1 Mac), the new Voice Control feature (found under Accessibility) is excellent, much more accurate than Apple's previous attempts, not limited to x number of words or seconds, and in most ways a very useful alternative method for those of us who like to dictate to our Macs. It's possible to add Accessibility to both the Menu Bar and the new Control panel, but it would be nice to be able to have the specific button for Voice Control without all the rest. And I'm sure users who have to manage with other ability challenges would equally appreciate the ability of being able to choose from and simplify from the list of options.
But this is a small gripe. Voice Control is excellent, comes free with the OS and looks like Apple have finally put some work into a feature that has been bubbling under for, well, decades now. Play around with it. It's worth the time and effort.