I may have missed the notice, but the latest information I have seen is that High Sierra is the latest Mac OS that Wolfram officially supports. I installed Mojave on my laptop and it seems to work, although I do get occasional notifications that Mathematica is not optimized (rather than the one-time notification that occurred with High Sierra).
The first question I have is whether Mathematica under Mojave is supported by Wolfram. The next question is when will a 64 bit front end be released. I am concerned that when the next version of the Mac OS is released there is no guarantee that any 32 bit code will have a chance of working.
Yes Mojave is supported. Version 12 is fully 64 bit and will come out soon, though exact dates are not known by me, but think months, not end of the year…
In fact, I already have a prerelease version for testing that is fully 64 bit.
Many thanks for the update, Sander.