And here was me thinking I spend the extra for a Sony on the next TV as they appear to 'more stable'. But well...
My initial instinct is that some sort of hardware is failing (storage, maybe?) but it was quite slow to begin with, so it's plausible a software update is the cause.
Any ideas what could fix it?
At home I have an non smart LG with an Nvidia Shield.
The IR remote, in particular, might be a solution for your in-laws' TV, as LG-compatible IR remotes are "plug-and-play" and available for less than $10 (avoid "service" remotes for this application, as they include a button that makes it easy to accidentally factory reset the TV, which is both annoying and, in the case of OLED TVs, maybe even potentially harmful[2].
RS-232 is particularly nice for tinkering with one's own TV, as it allows you to disable the OSD entirely, completely neutering all smart TV functions and pop-ups until the TV is turned off (or OSD is re-enabled via RS-232), and also includes video and audio controls not available on any of the IR remotes I've seen (brightness, contrast, bass, treble, etc.).
Along with a 4-port IR-controllable USB switch[3] and an audio interface with a TOSLINK input[4], I use the RS-232 functionality as a basis for my desktop "KVM", with inputs, brightness, power, and volume controlled with an Apple Siri remote paired to a Mac.
The only times I touch the menus are rare cases where I actually want to use the built-in smart TV apps (viz., for 4K video from services that don't support it on Mac or PC).
[1] https://github.com/jasminetroll/LgTvControl/blob/master/Docu...
[2] Source: unconfirmed Internet claims that the button resets a panel refresh timer that may lead to burn-in and warranty invalidation, which seems crazy for something that could be triggered without confirmation by a simple IR command one might accidentally mis-program into a universal remote by mistyping a single number.
[3] https://www.amazon.com/Cable-Matters-Sharing-Computers-Perip...
[4] https://babyface.rme-audio.de
Which is awesome and highly recommended, but for the present application any USB audio interface with low-latency monitoring and TOSLINK should work as well (and if you don't care about mixing the currently active HDMI audio source with other audio like I do, the volume on the TV's built-in speakers and non-digital audio outputs is controllable via RS-232).
To be fair, we don't use broadcast or cable, and use an AppleTV. So it's run as a dumb set for the most part. All the people complaining here seem to be using the built-in OS and tuner.