You can use a relatively cheap Pi as a NAS (network-attached storage), and possibly add Kodi media server capabilities (useful for smart TVs). Check if that model supports a sufficiently fast disk interface (USB 3.0, SATA etc.) and Ethernet (100 Mb/s or better if 4K is required). Boot from an SD card and use a 2TB+ HDD (1TB could be enough if you barely store anything).

I don’t know which Pi models can smoothly play HD video without overheating, I don’t own any. But those that can are likely a lot more expensive than old PCs you could use otherwise. I would just get a cheap one for a NAS and probably some other common network use cases (web server, Pihole etc.)