Syncing pst-files via OneDrive or Dropbox
Can I put my Outlook pst data file in OneDrive, Dropbox or other cloud based storage solution and use it as my active Outlook pst file so my two PCs can both sync and use the same pst file?
No, it is not recommended to use a Cloud storage folder for your active pst-file.
However, you can place a copy of your pst-file there, so you'll create an on-line backup copy too.
Syncing will corrupt your pst-file
Due to the active connection and lock Outlook has on the file, OneDrive, Dropbox or something similar like Google Drive, will continuously try to upload the file and thus use a lot of network bandwidth. It is very likely that this will end up in an incomplete or otherwise corrupted online copy which will sync to another device and/or back to your computer and result in a complete loss of the pst-file.
Even when you were to use OneDrive/Dropbox as an intermediary to copy over the pst-file between multiple computers (replacing the older local pst-file in another location), this could still lead to mail profile corruption and rules not working.
If you really want to have 2 PCs in sync, it would be better to look at using an IMAP, Exchange/Microsoft 365 or Outlook.com/Hotmail account type instead of POP3.
To still achieve it with POP3, you'll need to use a 3rd party add-in. Several are listed in the Quick Tip Sync via USB drive and also contains solutions for syncing via the Internet or local network.
Note that you can also use an Outlook.com account with your own current email address.
OneDrive or Dropbox as a pst backup location
Theoretically, you could use your OneDrive/Dropbox as an online backup location. You would then backup your pst-file to your OneDrive/Dropbox folder and then have it automatically sync to the cloud storage.
However, depending on the size of your pst-file and the network limitations set by your ISP, on-line storage space (OneDrive, Dropbox or something similar) might not be the solution at all.
For instance, upload speeds are often up to a factor 8 slower than your download speed and the amount of data which you are allowed to download/upload could have an upper limit too. Uploading a 1GB pst-file could then take a long time and daily backups will probably make you reach your monthly upload/download quota quite quickly.
If you really want to have cloud-based backups of your mail, consider using a mail host which backups the mail for you such as Microsoft 365 Exchange Online or ask your current mail provider about their backup and restore policies (how long back, how long a restore would take, how much it costs, etc…).