Yes you can - sort of.

If you want to import historical mileage from QB desktop to QB online (as I did), try this:

(1) In QBD, run up the Mileage by Vehicle Detail Report (Mileage, Mileage Reports, Mileage by Vehicle Detail)

(2) Choose the time frame for the report (I chose All)

(3) Under the Excel menu, choose Create New Worksheet

(4) Give it a name and IMPORTANT - choose "Create a comma separate values file"

(5) Now open the file and massage it so that you have the following column headers:

Date, Type, Trip Purpose, Vehicle, Start Address, End Address, Distance, Deduction, Logging Method

(6) I used the following example info in mine:

01/04/2021, Business, Site Visit, XC12 ABC, NA, NA, 175, 0, Manual

(All rows in my file had Business, Site Visit, XC12 ABC, NA, NA, 0, Manual column entries, only things changed were Distance and Date)

(7) In QBO, go to Mileage, click on arrow next to Add Trip, then Import Trips

(8) Select and Import the CSV file, and you should be good !

Why on earth Intuit couldn't add an import of mileage from QBD is beyond me. But then I've just moved to QBO and I'm starting to find it's limitations. Already looking for an alternative....