Jellyfin Casting and VPN

[BlissSol]

So I've never dug into the technical aspect of Casting (to a Chrome cast) - and ive never used it myself as ive never had a need...  So sorry if this is stupid question;
So Im wondering if it would be possible, when using a Split tunnel VPN with Jellyfin (in web browser) being accessed via the Split Tunnel - to cast this to a local TV (with Chromecast)?

To explain my setup and everything more...
I'm running Jellyfin server on my Win Server 2016 box.  Win Server is configured with DHCP, DNS, AD, IIS etc..  The Server also (currently) houses about 10TB of media storage.
I have a small QNAP NAS running on my network, setup with OpenVPN app (and thus obviously port forwarding configured on Router).

I actually use Jellyfin for kinda 2 purposes myself...
1) TV's in my house are powered with either a HTPC or Raspberry Pi - these all run Kodi & using the Jellyfin plugin for Kodi essentially Jellyfin is the backend server for Kodi.
2) When im away from home with my laptop, i just connect the VPN & access Jellyfin thru the browser.

** The Server has old AMD FX-8100 CPU, but has a Quadro T400 Gfx... so outside of like 4K HEVC video's, the Gfx card can handle re-encoding most things where needed & this is working.

Anyway... im trying to setup a friend with access to my Jellyfin ~ and they heavily use their Chromecasts, as the TV's are so old that either they're a 'non-smart' TV (No OS / No streaming) - or the TV has something like Android 4 (so streaming apps no longer supported & deprecated).
This friend is getting a (old)  Surface Pro 6 to use instead of currently either using their iPhone or old Galaxy Tab for casting.  The Surface Pro would also be replacing their current (old) Dell laptop.

So thus my thought & what im pondering - if my friend connects the Surface in their house to my (Split Tunnel) VPN so they're accessing my Jellyfin thru the VPN but can still access all 'local' network resources, would it be possible for them to cast Jellyfin (browser) to their local TV\Chromecast?
(I know at least with Split tunnel VPN's, i could access a website via VPN as its an intranet site on another network, while still being able to send print jobs to my local networked printer).

** Note - i do realize about SSL\HTTPS requirements for casting, which my Jellyfin isn't currently doing.  But i thought i should try to figure if you could cast with a Split Tunnel VPN before bothering with SSL.

[mutha]

I have just seen this mate and I hope you have sorted this by now - however, I am surprised at how complex a route you are taking.
IMO
If your primary requirement is as stated: "Anyway... im trying to setup a friend with access to my Jellyfin" and you friend has: "TV's are so old that either they're a 'non-smart' TV (No OS / No streaming)" and we can assume your friend has an internet connection.
Then I suggest your friend grabs an Amazon firestick adds the Jellyfin client and you set up a VPN for them. Far less break points.