I am using Outlook 16.4x with an Exchange account and all is well. Recently, I created an .olm file by using the "Export..." function and unchecking all checkboxes. This gave me the empty .olm. Afterwards, I "Import..."ed the same .olm again, and it showed up as a folder labeled "On my computer" (in German "Auf meinem Computer".
I created a subfolder in that, and moved some of my mails from my regular online account into it.
So far so good. Right now, even after closing and re-opening Outlook, that "On my computer" folder is still there, and as far as I can tell all the mails are also available. In that regard, everything is fine.
Where are those files stored? The .olm I mentioned above is about 2KB in size. While Outlook does not offer me any way (at least that I can tell) to view the size of that "On my computer" folder, I moved a few thousand mails there which certainly are larger than 2KB. I can sample those mails, and all seem to be there... somewhere.
Obviously I misunderstood the "Import..." command - it seems to import the contents of whatever .olm I specify (in this case, an empty one) and create that "Local" hierarchy; it does not seem to mount the actual .olm like the Windows client would mount a .pst file, where you can work with it, add more files and such.
How do I find out more about that? Right-clicking all the folders starting with "On my computer" does not offer any information, just very basic actions (much less than my regular online Exchange account within the same Outlook client).
Bonus question: I wanted to selectively export a subset of mails into a big file for offline storage, in the first place. I was not comfortable using the "Export" function - I assume it would have exported all mails, since it only seems to have a "yes or no" selection. What is the proper way to do this in the future?