VLAN not extending internet coverage

Hi all,

To give some context, the basic architecture of my network consists of a router feeding into a firewall. This firewall connects to a first switch, which is trunked towards an additional 2 switches than comprise the majority of our ethernet connectivity.

So, to the question at hand:
I'm in the process of adding a device to my network which requires a direct line to the internet. To do so I'd like to not have to deal with firewall shenanigans, and thus I decided I would create an isolated VLAN that can still use the existing inter-switch trunks. This VLAN would allow me - in theory - to only have to plug a specific port on my first switch straight to my router, which would bypass my firewall. Then, after using the existing trunks to reach the switch closest to the new device, I can simply run a cable from a port asociated with the correct VLAN to the device.

Anyway thats the context. The difficulty I am having currently is that no matter what I try, the ethernet connection from my router to my switch doesnt extend my internet coverage. In testing the cable, I receive internet at the end of the cable I plug into my first switch, but don't get anything in the corresponding VLAN when plugging into another port of the same switch associated with the same VLAN.

I'll freely admit that I'm fairly new to the whole network management job, so if I've gravely misunderstood what something is used for…. well lets just say I'm sorry in advance!

Heres a few screenshots of my current configuration if it they help:

The current configuration on the new VLAN, with port 3 being my trunk line, and 17/18 my direct connections to my router. 17/18 are solely associated with VLAN103, wheras 3 - being a trunk - is tagged in pretty much everything else:

I have not activated any port isolation, as - from what I understand - this would prevent any trunks from working, which would defeat the point of what I am trying!

I have attempting to create a PVID for ports 17/18, which seems like it could have been a fix according to other forul posts, but this did not seem to fix the issue:

Any and all suggestions are welcome, thanks in advance!