All the models I've seen that did this used USB HDDs that were encrypted and no one ever found a way for the content to play on anything but the TV it was recorded on. Also, many of the TVs forbid, denied recording from HDMI sources.
As such this is a pretty much dead technology. Most folk, once they reveal what they want to achieve end up on DVRs.
What 2019 Smart TVs support external USB recording?