Can I have internet on a router that has a LAN-BRIGTH with the same network that is on the WAN that belongs to the ether1 port
I think what you are asking is if you can have the same IP subnet on the WAN connection as on your LAN. If that’s the question, the answer is no.
Need more details for sure.
@k6ccc is right in his answer but there are so many other ways you could have explained this.
Draw a diagram of what you want to achieve maybe and we can help?