March
March
What model of box does your dad have (best to check the underside) and how recently has Netflix worked? Does it have the '4K' logo on the front? If yes, it should be an Arris VIP5602 or 5662 or Technicolor UIW4001 or 8001. If it doesn't have the 4K logo and/or isn't one of these models, it is likely an older HD PVR or Digital Box. Netflix removed support for their app on HD boxes in July 2023. There would have been on-screen messaging and emails back in the spring and early summer.
If he's on an HD box, he'll need to upgrade. If he's on a 4K box, I'd start with a reboot of modem, then PVR, then all boxes before calling tech support.
March