New pc with win11 outlook2021 creates .ost files how to connect past huge .pst files ?

Hello friends, I'm in a big trouble! With a simple trick Microsoft has made suddenly unavailable to me more than 10 years of my .pst outlook files! Having recently bought a new pc with windows 11 home and installed my old Office 2021 professional I have tragically discovered that outlook files are now generated with the .ost suffix ... leaving me unimaginably astonished at the incredible loss of all my previous outlook in-and-out messages! Having luckily saved in a system backup my old outlook and archive files Is there any quick and hopefully simple solution to such a crime? I'd be really grateful to anyone who can help me to solve this fully unexpected problem! Thank you! Antonio

Dear protonLeah, I CANNOT SEE any toggle button on my outlook screen! Screenshot attached. If this becomes available to me
it would be a wonderful solution ... but in this case shouldn't I first copy my old .pst files in the path:
C:\Users\...\Documents\FilediOutlook\Outlook.pst?
Thank you very much for clearing these additional doubts. Antonio

Please, anyone willing to clear my additional doubts? many thanks ... Antonio

On my pc is installed OUTLOOK from OFFICE PROFESSIONAL PLUS 2021, Vers. 2406, Build 17726.20160.
Will this help?

[ATTACH]87Screenshot (6).png5948[/ATTACH]Screenshot (6).png

I do not see any of my past years messages!!!

That toggle button is a giant LETDOWN ...
I've attached a screenshot of the result generated ...
I begin to fear the loss of my 10 years of 5 account messages
3 personal gmail , 1 hotmail, 1 icloud) ... who should I kill for such tragedy?

I can't read the messages in your screen shots, but can't you just install another mail program which can read those earlier .pst formats?

Hope this helps.

Pete

Does this help at all.

https://support.microsoft.com/en-us/...2-f331f60e2790

Dear friends as suggested by the ByteMarks link I have attempted the Import amails from an Outlook .pst file ... but it failed ... so since no other satisfactory solution is suggested, unlike to what I was used to (one single inbox for all accounts current and past mails), I have to settle for 5 different account webmails, which, even if not all, at least they seem to make available several of my past mails ... an uncomfortable solution, but so far the only one available to me! Although unluckily the desired goal has not been achieved nevertheless I wish to thank heartily everyone who has helped me in this matter ... working with you is always a great pleasure! Antonio