Hello @Anonymous ,
Thank you for reaching out.
Yes, You can link up to 10 virtual networks to a standard ExpressRoute circuit. All virtual networks must be in the same geopolitical region when using a standard ExpressRoute circuit. If you are using Local SKU ExpressRoute circuit this is not supported. Please refer to screenshot below for scope of access for different SKU Circuits. You can go through this FAQ for additional details.
You can refer to this documentation for implementation. The circuit owner creates an authorization, which creates an authorization key to be used by a circuit user to connect their virtual network gateways to the ExpressRoute circuit.
Hope this helps! Please let me know if you have any additional questions. Thank you!