I think I've found the solution to this annoying problem
By default, the setting for 2FA is "Off" but QBO annoyingly asking to enter 6 digit code via SMS or email still.
What I did was; I turned on the 2FA, have it completely setup. Then I turned it off again. After that QBO no longer asked for 6 digit codes. Just username & password after that.
Hope that helps!
