As it is possible to create a network using just a switch without a security appliance, is it possible to feed that switch dirty internet and use it.
Yes as long as the default route is your ISP's router.
I have always setup with a Mx or a Z1 device but a layer3 MS switch is capable of running on its own in Meraki network. I could create a network in Meraki based on ONLY a switch. But, can I use it as a flat switch ? I guess not. And as @alemabrahao mentions, where can I setup the uplink info as I can normally do on an mx/z1 device.
Configure a layer 3 vlan interface with a public IP then assign any switchport that vlan as an access port - that is then your uplink port
I assume this switch is going to be isolated from the rest of your network and isn’t your production network?
As already mentioned this is a security risk.
This is for any urgent case scenario where we are left with no choice and definitely for a temporary use case.