Sideloading has always been allowed, and that new "advanced flow" is something entirely decided by the OS so I don't think it has or will have any effect with GrapheneOS use.
It's actually recommended to get least of your apps as possible via the play store and use 3rd party stores if you are going for maximum privacy or de-googling.
It's actually recommended to get least of your apps as possible via the play store and use 3rd party stores if you are going for maximum privacy or de-googling.