While I agree with everything that's been said about using IMAP or Exchange (server side access protocols) rather than POP3 (where all storage is client side after download) I do want to note that it is possible to create local folders in Outlook itself even if you are using a server side protocol. I really, really, really advise against that for exactly the reasons on display in this topic.
It is unclear how the old folders were stored. If the old machine is still available the PST file can be imported over to another machine. But even if you do this, if these folders were stored under the Local Folders section, or otherwise stored locally, you are going to want to transfer them to reside as IMAP/Exchange folders under one of your accounts so this would not happen again.
Local storage and the POP3 client side email protocol are, very simply, best not used. They're holdovers from an earlier age and do not serve modern usage and access patterns, which means being able to get to your e-mail, all of it, from multiple devices and having them all stay in sync, at all well.
Brian - Windows 10 Pro, 64-Bit, Version 2004, Build 19041
The purpose of education is not to validate ignorance but to overcome it.