Ok. Here is a summary of everything that happened, what I tried, and what happens if I try that:
I was on firmware version 10.0.4 and decided to downgrade to 8.1.0 with ChoiDujourNXv102.
Everything seemed worked - it successfully downgraded to 8.1.0.
Then I shut down my switch, downloaded a tinfoil nsp, put it on the sd card, and booted the switch into atmosphere (using autorcm). Then I got an error. I don't know what it was. I restarted the switch, and launched it (again using autorcm, but i didn't boot into atmosphere, i just launched it normally). Then, I got a switch error. I can't remember which one it was, but something with 2001. I deactivated autorcm to see what happens if I start the switch without hekate. I pressed power off (inside hekate), but when i tried to start the switch again, nothing happened.
Now, my Switch is completely black and has no sign of life.
I charged it for about 10 hours to make sure it has power, but that shouldn't be the problem, because when it started to do nothing, it still had about 50% charged.
I tried holding down the power button for 10s, 30s, 1m, ... to force shut down, and then start it again, but nothing seems to happen.
I tried to launch it into rcm mode with a bent paperclip - nothing happened.
I tried launching it into rcm with a 3d printed rcm clip - nothing happenend.
Then, you guys said it might already be in rcm, and I should just install the drivers. When i plugged it into the pc to install the drivers via zadig, it didn't detect any device. I also tried to click Install Drivers in TegraRcmGUI, but after a restart of the programm, it told me that the drivers weren't installed, and it also doesn't detect the switch.
So this is were I'm at right now.
I don't know if the switch is on (and maybe inc rcm mode).
I don't know if it has battery or somehow the charging is broke.
I don't know if I somehow touched pin 4 when trying to boot it into rcm and shorted something.
So I can't just assume it's in rcm mode.
And to your question:
You are in the rcm. What happens if you only charge the console?
Nothing happens. No indicator on the screen or anything. But again, I don't know if it is even in rcm.
One thing I tried is running it trough a plug that tells me how much watt the device plugged in is using, and it told me it's drawing 2W. I can't tell you how accurate this is though, but at least (I think) it should mean that the charging port is not broken.
So, what is there that I can still try, or is there anything I can do to see if my switch is even alive?