Without having had a lot of time to work on a switch myself recently I can't be sure, but it sounds like your analysis is spot on. The description of your problem pretty much rules out all problems except the screen and cable. As the screen gives a solid black color instead of a weird color scheme or pattern I believe it to be fine, and the culprit to be the cable, but it might be easier replacing the whole thing anyway. that is up to you. I woud suggest trying to find a replacement cable first and seeing if you can get it working with just that. Make sure you read through the full teardown here on Ifixit. While the switch does have some repairability, it's still easy to tear those ribbon cables (even they did it). good luck on your repair, and I hope you'll get your switch working again in no time!

How much ram memory is installed in the pc? windows 10 uses slightly more ram than previous versions, unless you already were running windows 10 before, in which case I would suggest going through the task manager and seeing what is using up the resources of your computer. Are there programs running in the background you don't need? Also did you get a good copy of windows. I won't harp on pirating or whatever, but many of the torrented versions of windows are unsafe, and may be running software in the background. (Some people have the windows install run cryptomining software in the background, which would make your computer really slow as it is rather resource heavy). If you have more than 4gb of ram, you should be ok, and it is most likely some form of software infection. I would suggest reinstalling windows from a verified source. Good luck!

Without knowing the specific model I can only guess, but I would think the display cable connecting the screen to the motherboard has broken. With some care it should be possible to open up the laptop and check it to make sure. The LCD screen guide for your laptop explains how to open up your laptop and find the cable (as it needs to be disconnected to replace the screen). In your case the screen will probably be fine. Replacement cables can be bought online (I think I saw it in the ifixit parts store, although you may be able to find it cheaper elsewhere). If you want to make sure the computer itself is still fine, find a tv or monitor and connect your computer to it using an HDMI cable. if your screen is visible on the external monitor, then the issue lies either with the cable or the screen. Since the screen did not take a hard hit the cable is the most likely bet. Happy fixing!

I'm sorry but looking into your question a little makes me believe that it is highly unlikely to work at all. Unlike computers for example, most TV's are not modular, meaning that you can't just desolder a few parts and throw in something new. On top of which HDR also requires specific firmware. If you manage to get a TV working from mixed parts, which already seems highly unlikely, even if the internals of the 2 models are highly similar, there is no saying the required software will be willing to run on it. I'm sorry, but I'm afraid that this is an area where DIY'ing just isn't worth it. You're more likely than not to break your TV, and if you manage to get the parts, get them installed properly and have it all be compatible there is still a chance that the software won't run, meaning you still won't have what you wanted. I know this is probably not the answer you were hoping for, and I wish you good luck with any ohter projects you may have.