@Toto77fr
Hello, what is the model number of your device? Is it Archer VR2800V?
May I know have you purchased it yet? If you haven't get it, considering the dongle is not listed in the compatibility list, it is not suggested to use them together due to potential loss. And the 3/4G router mode is a supplementary function.
If you have purchased it already, you can give it a go by plug the 4G dongle into the USB port of the router and try to configure it; if we cannot figure it out, I'm afraid that there is not much we can do, you can return it and get a 4G router.
Good day.