I think your installation is OK. There are some known changes regarding button definitions since LE 9.x.
Your button press is activating two actions at the same time, which indicates overlapping definitions.
So, my first advice is to uninstall the keymap editor add-on, and do all definitions manually.
Use the suggested place for remote control definitions, which is /storage/.kodi/userdata/keymaps/remote.xml .
Give me a feedback how your code acts under the described conditions.
Which hardware do you use?
Where do you have the mentioned code stored?
What's the remote button behavior without that code?
I assume you want to shutdown instantly when you press the button. Edit line 4 this way:
<power>shutdown</power>But I want to add refresh rates not reported by the device. There´s any way to do this?
I'm not sure. I gave an advice here, but I still have no feedback. Adding res. / refresh data should work the same way.
This is how it works: The output device is telling LibreELEC all supported resolutions / refresh rates (goes automatic over HDMI).
At the LibreELEC settings you can select one of those resolutions / refresh rates as your default.
I only see the Odroid C2 at the download page, not the N2. I think an RPi 4B is the better choice, if you want to use that special Amp HAT.
Yes, I always get the selected res./refresh when I'm switching to my RPi. Something about Swedie's HDMI negotiation between TV and NUC goes wrong.
Removing resolutions / refresh rates from guisettings.xml might be a solution. This settings file has your preferred and TV-supported resolutions / refresh rates. Remove undesired refresh rates from the TV-supported list.
Problem: guisettings.xml will be updated by LE with all available resolutions / refresh rates your TV is offering. If guisettings.xml will be updated only at boot time (I'm not sure about it), overwriting it with your custom version should be possible by using a command at autostart.sh.
what settings are needed for 4k 60fps
Read here.
What's the output if you do this from SSH?
/storage/.kodi/addons/service.hyperion/bin/hyperiond.startWe got a couple of threads about Hyperion, use the search function. Read here for a RPi 3 success story.
Remove the MicroSD card and read the log file (kodi.log).
Usually the card has errors, and disk check is incorrect.
Use GParted for a detailed check or repair, if necessary.
GParted is for advanced users only, buying a new card is easier.
I had a short look at your log files, and I suggest to try the default skin.
Always use the default skin when you post a log. Custom skins are known trouble makers.
LE 9.0.2 runs fine on my RPi 3B+. I only have save mode issues with current 9.1.x builds.
I have the lightning bolt, too, since a couple of days (old PSU), and disabling the rainbow screen still works.
If not, is there another way to make analog audio via USB work?
Don't forget to activate analog audio at the LE audio settings ("HDMI + Analog" activated).
Check the presence of analog audio on the headphone jack of RPi.
If it doesn't helps, check analog volume.
But I give it a try and let you know if it worked.
It worked for me. 
Is it a matter of tweaking settings in LE or Kodi? I'd prefer to do this from LE if possible rather than having RetroArch terminate Kodi.
I don't know the implementations, too, but I think there are no helpful tweaks. The LE game engine is a young feature, and probably not optimized yet.
I don't know your hardware. For my Raspberry Pi I usually plug the MicroSD card off, and edit stuff on my Linux PC.
Here are instructions how to edit config.txt otherwise.
