New Outlook won't open .pst files

"When did this idea of simple convenience become obsolete?"

Lack of .pst file support makes the new Outlook unusable for me. Can't understand what Microsoft is thinking.

Unusable for me also, but I know perfectly well what Microsoft is thinking:

"We want to force you to store your entire life history on our servers. We can charge you $$ for space, increase the price every year, and also 'mine' it to manipulate your spending and other behaviors. Oh, and we will also hand it over to the government on request."

Or more succinctly:

"All your data are belong to us." (as uttered by a poorly translated video game)

I recall reading or being told at some point that Microsoft does not intend for the new Outlook to replace the professional edition that has PST capabilities. Rather, it's meant to be a streamlined version for casual users. That said, I don't appreciate that the new version was offered to me and it's said that it's a worry-free test that can easily be reverted back...only to find that the toggle disappears and it is, indeed, NOT easy to switch back to the regular Outlook.

Microsoft E-Discovery exports as a PST how do you do compliance reviews on exported data without a PST?

For me, as well as perhaps many other Outlook users, access to older PST files is essential! They have helped me for years to keep my contacts and emails organized. I have to keep using them for both personal and professional reasons. Re-supporting PST files in the New Outlook is highly recommended!