First: You've been mixed different topics into one thread. We don't like that one-thread-fits-all thing. One question - one thread.
...make the display of my A/V-Receiver show "Multi-In". Is this the same as Dolby Digital?
In the good old days of the internet, the answer would be: RTFM (read the fuc*ing manual).
Anderssen Well, christmas is the time of miracles 
. You're right, on a non-4K device a 1.4 HDMI cable should be fine. Those 2.0 / 2.1 HDMI cables have better shielding, so I think that did the trick for you. I'm happy that we finally solved it. 
It's not just you don't have "apt-get" on LE, you also have to hack the kernel:
The next step is the part where we hack the kernel! This is what's going to enable us to get 8 channels of sweet, sweet, high resolution audio out of the Pi via HDMI.
The answer is: yes, it's possible - if you're an Amlogic kernel hacker. I don't think somebody else will do that work for you, because it's so unusual. Your question assumes that you are no kernel hacker. So my advice is to buy an RPi, follow the instructions and don't use LE.
PS: HiassofT currently builds an audio-optimized LE for RPi4. If you're very lucky, he could help you, but surely not on Amlogic.
Maybe it's a good idea to start with a fresh installation on another microSD, because your current installation is packed with add-ons.
I'm using the DAZN add-on from the "Kodi Nerds" repo, and I'm in Germany. Maybe one of those facts makes a difference. The rest is pretty close to your setup (LE 9.2.6 on RPi3B+).
You found the right guy, I had the same error a couple of days ago 
. Solution: Uninstall the DAZN add-on (including config data), switch LE's GUI language to English (US) and install / login DAZN under that language. After successful login you can switch back to your original GUI language. Maybe the add-on developer is from the US, and hasn't tested other language environments.
de-interlacing is disabled for all videos. Hardware acceleration is switched-off. Nothing changes. However, here's an interesting thing there are no problems with sound in bluetooth headphones. This is a clear HDMI problem .. Maybe, even the HDMI-MicroHDMI adapter is cheap. Maybe the TV is cheap (unnamed). I am switching temporarily back to RPI3 (it is really problem-free)
Thanks again for the feedback! Can you check the standard of your HDMI cabling please? It has to be conform to HDMI 2.0 or 2.1. Otherwise it could be too slow for 4K. It's a common mistake of RPi3 -> RPi4 switchers not to update the HDMI cabling.
Adding total_mem=2048 to config.txt does not fix the problem for me.
Deactivate de-interlacing.
You have another repo, which is a bit hidden at the log:
2020-12-03 15:19:09.039 T:1936779712 NOTICE: ADDON: hellyrepo.kodi v0.2.6 installed
Maybe you get add-on update errors from hellyrepo, and those errors avoid add-on updates from other repos:
2020-12-03 15:21:33.690 T:1566417792 DEBUG: Curl::Debug - TEXT: Connected to flex.vodacom.co.za (91.241.95.156) port 80 (#1)
2020-12-03 15:21:33.690 T:1566417792 DEBUG: Curl::Debug - HEADER_OUT: HEAD /err/?err=404 HTTP/1.1
You have to describe your HDMI cabling more precisely. I still don't understand the role of LE on your setup.
You were talking about a new HDMI cable. Are all of your used HDMI cables conform to 4K (HDMI 2.0 / 2.1 standard)?
Klojum means, if you want to post a longer log, use a link to a service like Pastebin.
It's not our goal to release a mature internet browser. That request has already been answered - use the search function. You will also find answers about Netflix and YouTube, if you search the forum.
We have a Wiki, which answers LE questions. Because there are so many add-ons, we currently can't cover those topics on Wiki.
The repo's depend on your needs. I'm using the "Kodi Nerds" repo for instance. Make sure it's a legal repo, otherwise we stop support.
OK, then I can't help anymore, and all you can do is to find the right skin.
Often users are unable to add an entry to the favorites menu, because they don't have the context menu button at the remote control. To map the context menu button to the blue remote control button, add this remote.xml to /storage/.kodi/userdata/keymaps:
<keymap>
<global>
<remote>
<blue>ContextMenu</blue>
</remote>
</global>
</keymap>After file creation, reboot and try to use the context menu to add menu entries to favorites. You can't add all menu entry types to favorites (this is on my wish list), but maybe it's enough for your needs.
On Estuary skin the Favourites menu was designed to store shortcuts. Using other skins can make trouble, if they are outdated, which is pretty often the case.
nano /storage/.cache/connman/settings and edit the value of SSID. I only found an outdated doc, but maybe it helps: Click!
Loaded with banned addons and porn. You'll get no support with that stuff installed.
Correct - closed.
Can I simply edit whatever file is in the directory, mglae, or do I need to create a new file/etc?
It's part of the cache folder, so don't be shy. 
Maybe just:
Codeclient = Client("P1") #create new instance client.connect(broker_address) #connect to broker client.publish("house/main-light","OFF")#publish
PS: Or you have to start the service before you can use mqtt.Client("P1").
