With no external sign, electrolytic caps do lose capacity. This info is in the datasheets and on the web. Since it sounds power related, you could take a gamble with a new power board. The next board is the big one (main board.)
But try something. Disable the smart part of the TV and see if it stays up. Sometimes that works and we advise getting a Roku box or stick.
i have been reading all the answers to the LG smart TV questions on this forum.
mine is a little different to all,
i turn on the tv and it will work perfectly for hours, then boom! just goes off and all i have is the stationary LG logo flashing on and off.
if i leave it plugged in it never changes
But if i unplug it for a few hours 9 times out of 10 it will work again for anywhere from 1 hour to 10 hours.
obviously the powering down by unplugging seems to be the key to the diagnosis.
i was told it is probably a capacitor in the mother board?
but ive looked and none look swollen
any tips would be really appreciated as my local repair guy want $90AU just to take a look