Accessing Outlook .pst files in New Outlook

There are multiple free and paid tools which can open and convert PST files.

The fact that Microsoft is not willing to add this function to the "new" outlook is just malevolence or greed, in my opinion.

I have never deleted an email for over 20 years, and I still have access to them. As a note, moving from a cloud solution to another, the only reliable historical data is on my drive and it's backups.

Can I go back to the last version of Outlook that allows use pf PST files? Or is there another platform of email that does allow use of PST files? I understand that Outlook and other programs make changes to their systems ... to sell more software ... but the CHANGES MADE TO THE MOST RECENT VERSION OF OUTLOOK are not appreciated (by me at least).

Here's the information from current roadmap item for adding PST support:

You are not being clear for me. Will one move their .pst files "Back" into the old classic outlook, and then into the new Outlook, or just move the .pst files "forward" into the new Outlook?

I have a similar file size problem, although my total file size is "only" 29GB with over 3 dozen .pst files (many of them with many subfolders).

However, I have two serious additional problems:

(1) I am a contract technical editor, and some of my clients email me highly confidential technical material. For security and patentability reasons, they require me to ensure that their emails are securely held on my system only and are never stored on an outside server. How can I access all my important .pst files with the new Outlook, without losing or betraying(!) these clients?

(2) Through some sort of inadvertent keyboarding error that happened while I was typing an email to a client late at night, I unintentionally and unwillingly gave permission for Microsoft to update my Outlook installation immediately. There was no "Are you sure?" pop-up message. As a result I HAVE LOST ACCESS TO ALL MY .PST FILES, AND I CANNOT FIGURE OUT HOW TO GET ACCESS TO THEM AGAIN.

These .pst business files are all still intact in a folder within my desktop, but I I don't know how to access their content with the new Outlook. Also, I may lose some important clients if I cannot prevent the uploading of their files to a Microsoft server in the cloud.

I'm no email tech expert, but can see no way to fix this situation using the new Outlook.

To provide a temporary solution, how can I revert back to the old Outlook?

Or, after being a Microsoft email user since the 1990s, do I need to immediately migrate my email system to a different email provider that can actually meet my business needs???

This problem is time critical: please answer as soon as possible. Thanks.