The ONT will assign one IP to the first device that connects. Every other device will look for a DHCP server to get an IP and the ONT will not allow them to get an IP.

You will have one device with and IP and everything else will be stuck.

This is why you have a router. A router has a front end to accept that one IP address and then use its own internal DHCP to allow everything else to access the internet, THROUGH the router. It is a one to many situation. A switch does not have this capability.

Can you?

Yes.

Should you?

Probably not.

I have $6000 worth of burned out electronics to help you understand that this in not the best idea.

I’d use fiber instead. If you are not using fiber and you insist on going with copper you need a really good burial AND really good surge protection on each end.