Thanks for all your help
So I succeeded with updating. I decided not to wipe the sysnand for an emunand setup. Because I still was in the middle in multiple games and I didn't want to lose my saves.
When I finish them I problably will wipe it all and start over with an emunand.
I wrote a small guide how I did those steps. So maybe handy for the people who also kosmos-ed their switch 2 years ago and forgot some of the steps. And also as just a little update of the stuff which changed. I was so out the loop and stuff changes fast.
Ok, this is just for an update for a switch playing Offline, from kosmos to deepsea who don't need emunand as of december 2020 how it worked for me.
Your savegames will stay. Also your installed games will stay.
1 Take out your sd card from the switch, put it in a pc.
Go to:
https://darthsternie.net/switch-firmwares/
Downloaded firmware, zip and unzip it on the sdcard.
I did not choose firmware 11, because some homebrew I could not run yet. And got 10.0.2 for compatibility.
2 Next step, go to DeepSea site and download it:
https://github.com/Team-Neptune/DeepSea/releases
Unpacked the deepsea zip on your pc. Checked similar folders on sdcard.
Moved your current folders on the sdcard which are named the same to something like 'Backup_kosmos' in case you want to reverse.
I moved:
-atmosphere
-bootloader
-config
-sept
-switch
-hbmenu.nro
To a backup folder.
Then I copied the folders from the Deepsea package to the sdcard.
3 You need 'sigpatches' or all your games will give errors when you startup. Just download it from the first post from:
https://gbatemp.net/threads/sigpatches-for-atmosphere-hekate-fss0-fusee-secondary-only.571543/
Unpack and copy the folders, it will overwrite sig patch files to correct places
4 Firmware update. Put your sd card back in the switch, bootup with tegra or your preferred method.
ChoiDujourNX still works, but is now considered old. Use Daybreak to update firmware, the successor to ChoiDujourNX. Daybreak is included in the Deepsea package.
You have to go inside the homebrew menu.
With Right Shoulder ZR button pressed and A on app like photoalbum gives homebrew menu in 'applet mode'
With Right Shoulder R button pressed and A on a game, will go to homebrew in a better 'app' modus
Applet modus is not preferred, I don't know why.
Daybreak is the first homebrew app, choose and just follow the steps. When it looks for the firmware, choose the location you unzipped it at the first step. Also choose fat32+exfat.
5 Get your allready owned backed upped games on it with your new firmware
From pc usb to switch.
On the PC I used ns usb loader, get version 5 here:
https://github.com/developersu/ns-usbloader/releases
On Switch with kosmos I used goldleaf, but included with Deepsea is NsaInstaller. Somehow goldleaf didn't work.
Set ns usb loader to Tinfoil modus, then they should connect. (also do the stuff with zadig first)
6 Problem after update, gamecard does not read
It's a protection so a gamecard will not update your switch by accident and destroy your fuses.
To enable the GameCard slot add nogc = 0 to the bct.ini
