I am required to enter the QST identification but my employer is in BC, Canada. I am claiming expense for my home office in Quebec only. My employer has no QST #

Try to enter 000000000TQ0001 as QST number (section Identification of the employer in the TP64.3) otherwise you will need to print and mail.

I’m having the same issue for my 2022 tax. A 10 digit number is required.  I’ve filed the same way for 2021 and never encountered this requirement.