Thanks for the update Toby, I have tired 4 different cables so far, one that came with the phone, Another MI original Cable, Oneplus 9 Original Cable and another Fast Data transfer cable. None of them worked.I resolved mine by trying quite a few different cables, I didn't think it would be the cable as the cable that came with the phone didn't work, but this cable has been working perfectly: USB C charging Cable TecMad USB Type-C
I'm not sure why this cable works but the stock cable doesn't, in theory they both meet the USB-C standard...
I don't want to buy another one now
With all these cables my Oneplus 9 connects to the same system absolutely fine.
Not sure where the issue is