Please be specific. That is, if your account is IMAP in Thunderbird, you can set up an IMAP account on your phone and see/reply to the same messages that are on the PC.

I have tried to export from the desktop to the mobile by using the QR code. Only the Outbox appears on my mobile. I then deleted that account and tried to load the email manually using the same setting as the Desktop i.e. IMAP etc Please advise why my inbox etc was not transferred.

I do not use Thunderbird on phone, so cannot give specifics on the export feature. If the account is setup with same parameters as done on PC, the full account should be there. Check to be sure your PC account is IMAP.

Yes, it definitely is.

Thank you so much for your help, David. Really appreciate it.

I'm not sure I was of much help, but maybe I served as a sounding board. I'm glad all is well. For me, setting up an account on a smartphone is worse than a root canal. :)