voidlinux still has the 390 drivers available. I'm sure others do too:
[-] nvidia390-390.157_6 NVIDIA drivers (GeForce 400, 500 series) - Libraries and Utilities [-] nvidia390-dkms-390.157_6 NVIDIA drivers (GeForce 400, 500 series) - DKMS kernel module [-] nvidia390-gtklibs-390.157_6 NVIDIA drivers (GeForce 400, 500 series) - GTK+ libraries [-] nvidia390-libs-390.157_6 NVIDIA drivers (GeForce 400, 500 series) - common libraries [-] nvidia390-opencl-390.157_6 NVIDIA drivers (GeForce 400, 500 series) - OpenCL implementation
I use mythtv (FOSS) and it's fine as a PVR (schedule, record and playback broadcast TV) with a SiliconDust HDHomeRun network-attached tuner. It also has playback for downloaded files but I prefer to use mpv for that. Mine is still connected to the internet and I use firefox/transmission for youtube and other functions.
No idea about plex or jellyfin.