Hello @Jamie-R-JR and welcome to the forum!
Detailed guide to set up OneDrive Personal with 2FA has some discussion of the general topic of two factor authentication. There’s sort of a hint there that it should ask once, however that might depend on whether a direct access to Duplicati OAuth Handler is done, or an indirect one done by clicking on the Destination link.
Another possibility is Sign in using App Passwords, although I’m not sure if Google knows your Duplicati yet.