Hi there
@
JJG10
Not sure if this is the 100% correct answer - but here goes.
Until Outlook 2016 or so all the data content in outlook was contained in a .pst file. If you use IMAP rather than POP3 then even if your mail was maintained on the server there were always some things that would be held on a local PC and these were generally in a .pst file.
Often people might want to save data from IMAP / EXCHANGE servers on to a local PC for archiving / copying etc and this data is in a .pst file even though the main OUTLOOK data files are no longer held in .pst files.
OUTLOOK/365 has loads of people converting from systems as far back as even OFFICE 2007 so compatability with the old .pst files is still maintained.
If you don't need these files then OK but they are good for archiving / copying to another computer.
etc.
I really wouldn't worry about the creation of a .pst file --if it's not needed it won't have anything significant in it and won't be large anyway. Just ignore it.
OUTLOOK 2019 / 2016 and /365 can all open, handle, read and write to .pst files without problems so you shouldn't lose any data converting from Office / OUTLOOK 2010.
Main data files now in OUTLOOK are I think in .osd files -- no idea -- I use OUTLOOK 2019 with IMAP and save any data from the servers into a .pst file which can be opened / read / write etc just as any of the other IMAP folders - the only difference is that the .pst file is stored on the local PC and not on the email server. The .osd files have info about the IMAP files on your email server.
I hope nobody here is using POP3 any more of course.
Cheers
jimbo