This maybe a silly question?
I have Plex setup on my PC (server) when I am running a movie from Plex to my TV does this use my ISP’S data allowance?
Normally not.
There may be a few situations where data are transferred over the internet but you’ll recognise them relatively quickly.
If there is no remote-access intended for your server (i.e. you want to stream from your server at home while being out of house) this is also relatively easily resolved.
If both the server and the client are on the same local network then the answer is no. All streaming on the local network is local.
There is some brief data transfer to Plex’s server to get your account info.
