New Outlook - PST file cannot reopen and PST search not working

The fact that PST B previously opened in New Outlook is important. Removing it doesn’t change its format, so that alone wouldn’t suddenly turn it into an unsupported PST. Classic Outlook opening it successfully also makes serious corruption less likely, although it doesn’t prove the file is completely error-free.

For the reopening problem:

1. Back up PST B first, then fully close both Outlook versions. Check Task Manager to make sure Classic Outlook isn’t still running and holding the file open.
2. If the PST is in OneDrive, another synced folder, or a network location, copy it to a normal local folder outside those locations. Try adding that copy in New Outlook.
3. In Classic Outlook, you can check the format by right-clicking the PST’s top-level folder and opening Data File Properties > Advanced. “Outlook Data File (97–2002)” indicates the older ANSI format. Don’t convert or repair the file just on suspicion; record the exact error New Outlook gives first.

For search, being able to browse a PST doesn’t establish that every search feature is available in your New Outlook version. Make sure the search scope actually includes the PST—searching the online mailbox won’t search a separate archive. If New Outlook offers searching the selected PST folder, test a distinctive word from a message subject you can see there.

If that still returns nothing, keep using Classic Outlook for PST searches and report the issue with your New Outlook version and the exact scope tested. Rebuilding the Windows search index isn’t a reliable fix for a New Outlook search problem.

I wouldn’t treat either symptom as proof of an unsupported format. Since PST A works and PST B worked before removal, the failed reattachment and PST search should be investigated separately. An exact support statement about PST search needs to match your current New Outlook release, rather than assuming feature parity with Classic Outlook.