It is an unusual question to ask, but you may be surprised at the answer.
Not just youtube
Streaming movies and youtube videos is often thought of as watching TV, but the question is based on not using any data. Playing of a USB stick maybe? – That is also possible and useful for playing favourite films when parked-up. But the question is specifically about television.
Freeview – the digital television
It is possible to attach a DVB-T2 (freeview/digital television) adaptor to the USB socket of your android headunit. The DVB-T2 adaptor needs to be connected to an aerial, just like any other digital terrestrial television adaptor or set top box. But with just the DVB-T2 adaptor and its aerial, you have digital television on your android headunit. No data connection, no wifi, no 4G needed and you are offered 100s of TV channels and radio stations, all in a digital format.
Connect the USB to your headunit and the aerial to the USB, download the app for the adaptor or find one on the playstore. Scan for channels and you are set to go.
We have used this adaptor in the past with good results. We particularly liked the supplied aerial that is quite compact yet still gets a good signal. Putting the aerial on the van roof gave the best results.