That was written for 9.0.0, if you downgrade to 9.0.0 and burned your fuse while you were on 11.0.1, you will run into problem booting, good chance your unit refuse to boot.
I didn't burn fuses in updating to 11.0.1 so downgrade was possible
Writing my experience here
so, I was on 11.0.1 and I downgraded my switch to 9.0.1 (I did almost everything using the homebrew AIO Switch Updater)
Atmosphere didn't help even with the kip linked here
Incognito RCM didn't help either
Migrated to ReiNx 3.0 (latest) , but didn't want to boot because of an error
then I've found a forum with the simple solution
"Solution for Error code 2002-2634 with sysnand firmware 9.0.1"
The only thing that I had to do is removing the Cartridge
After that luckily everything worked great in ReiNX
Hope this may help somebody in trouble