Doesn't apply to me. I have Outlook 2016 installed in addition to Outlook (new) app. 99.99% of the time I use Outlook 2016. I check Outlook (new) once a week or sometimes once/twice in a few months. Both apps are connected to the same mailbox, my work email. No other mail accounts in either app.
I believe what you described is how to install Microsoft Outlook/365 and Outlook (new). It sounds like the download is an ISO file which, when mounted, you'll get a virtual drive letter where you find setup or setup64 to run/install the software. If PST support on Outlook (new) requires Outlook/Microsoft 365 apps, that explains why I can't add a PST file in my Outlook (new) app. I don't have 365 apps.