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You can get a variety of TV tuners which can work with your PC, Hauppauge are a big brand. I'm not sure which are Linux compatible but plenty will be as lots of PC use them for HTPC setups.
Or you can get a network tuner like this https://www.amazon.co.uk/Silicondust-HDHR5-2DT-HDHomeRun-CONNECT-Tuner/dp/B07BFNRGN9/ which anything on your network can access. This will work with Linux (I use it with Ubuntu and Kodi on mine).
I don't have a TV: can I get a Freeview box to work with my computer (Linux)?