Are you getting connected to Wi-Fi but it’s just showing no connection or the connection is not working.

If so, that would imply your SSID and password are correctly set up at least.

Are the devices getting IP addresses? Can the devices ping the gateway if they are? Are they able to look up DNS?

Ask your college IT department or whoever is responsible for the network in the dorms.

It is possible and even likely that they have a MAC limit set on the port as well and if you exceed that the port can be disabled automatically.

A) I can guarantee you wasted money CAT8 cable for one.

B) You can’t split ethernet like you can a coax TV cable for example or even a phone line. You would need a splitter on both sides that would limit both connections to 100 megabits per second and you would still need an extra port on the the router or switch.

What you need is a network switch. It would plug into an available port on the router, and more devices can plug into it.

… Category 6a will get you 10 gig at 100m…

Category 8.1 (No such thing as just 8, just like there’s no such thing as 7), is for 25 and 40 gigabit at 30m, So at the distances you are talking there is no difference between category 6a and 8.1.

Likely your router does not support NAT loopback.

Thus, you will not be able to connect to your public IP in the port forwarded from a device that is behind your own router.

And that is correct that all devices on your local network will show is having the same public IPv4 that is what a net router does.

Use SFTP or FTPS, plain FTP should not be used.