FLAC is not “buried” it is consolidated equally among all the other audio exports in the latest Audacity.
The alternative would be to expand the old File>Export sub-menu to contain entries for all the available export formats (a route which IMHO Muse sensibly avoided
What Muse did with this was to simplify the audio export menu structure - a step which I personally think is good, as I hate seeing unnecessary menu-bloat in any app.
And actually in most earlier Audacity versions there was only ever a single export audio - it was only in later versions that the exports for (some, and only some) particular exports were added to the menu structure - so really Muse is actually reverting to the older, cleaner, simpler, menu structure.