My parents are about to get a new TV because theirs is faulty and they don't seem interested in repairing it. I'm going to be taking the faulty one from them and, because it's ridiculous that the TV only worked normally for 3.5 years, am very tempted to try a repair. It's an LG CX OLED from 2021, here's a description of the issue:

• When plugged into the mains, the standby light will come on and the TV can be powered on and used as normal. However, if too much time elapses after plugging-in without fully powering on (I don't actually know how long, somewhere between 5-10 minutes), the standby light will switch off and the TV will become unresponsive.
• When the TV is in this "unresponsive" state, the only thing that will bring it back to life is to unplug it from the mains and wait a bit (again, somewhere between 5-10 minutes), then plug it back in and turn it on. This happens every time the TV is plugged in, with no variation.
• The TV is fully functional when it's turned on, and there's no other issues with it at all.
• If the TV is turned back off (back to standby mode), the clock starts again until it becomes unresponsive.

So clearly there's some problem with standby mode. Some searching has indicated that other customers are frequently having this issue, and that replacing either the PSU or Motherboard of the TV will solve the issue. It's out of warranty, so I'm going to be spending money if I want to fix it. Replacement PSUs are about $250, and replacement Motherboards are about $350. I can only really afford one of these parts right now, so it's a gamble if I can't figure out a way to isolate the issue to one of the boards. I don't own a multimeter to test power, nor do I know anything about electronics, so I'm slightly fumbling around in the dark on this one.

There's always the alternative of getting up and switching the power on and off every time, which is significantly more convenient for me than it is for my parents because of room size and outlet placement, but I'd like to be able to use the remote as intended (and, as I mentioned before, it's ridiculous that the thing is falling apart after only a few years, it's a very expensive TV!). I could also... find an IR controlled outlet or something? I don't know if that's a thing, but you know what I mean.

I will end up using this TV regardless of whether or not I can get it fixed, because OLED is unbeatable, and it's not every day that my parents will replace something that isn't outright destroyed, but if you have electronics experience, or have had this problem (it seems like it's super common) any recommendations or help would be appreciated!

SOLVED
Bit of a long shot here because this is one of those issues where I search for the problem and you get a sea of replies like "have you checked the settings?" or "have you tried changing HDMI cables".

I just got a brand new LG OLED TV and I'm happy, but I've been watching Arcane on it and I notice jarring changes in brightness through the episode.
I'm playing through a native app (Stremio) on WebOS and it's not the source file, I've tested the same file on two different monitors and it's fine.
I went through the settings and disabled every autocorrect and "boost" capability the TV has to try and diagnose it, and the first pass did seem to improve the rate of changes, but it still happens maybe once every 5 mins of watch time.
From what I can tell it seems to be picking up particular colour/brightness changes in the source (Arcane is full of then being so vivid) and when it does, it just changes the brightness of the whole display.
I'm no expert here, I'm also colour blind, so I won't categorically claim it is definitely brightness changing, it could be contract or colour, I'm not sure, but it looks like brightness because the whole picture gets darker or lighter.

I wondered if it was actually flip flopping between SDR and HDR which honestly, it might be. If it is I have no idea how to fix that, as the TV seems to have no option to enable or disable HDR on native apps.

Any advice, thoughts, things to try would be appreciated. I'm technically orientated but I don't really know much about changing picture settings to be honest, I tend to pick the most basic/neutral setting and leave it like that.

Edit: I've dug out the old 4k firestick as suggested and don't get the flickering at all through that. Also running through the guide below helped make the picture look even better! Thanks everyone!
I might yet grab the service remote though and see if I can make the native apps work, then I can retire the firestick for good.