I figured manually rewriting firmware files using PC version of ChoiDujour should fix this ever since I royally screwed myself by updating my SysNAND.
I tried the following guide but somewhy couldn't continue as I got a different result than the file specified in the guide.
https://switch.homebrew.guide/usingcfw/manualchoiupgrade.html
This guide specifies I should use a keys.txt but says I could also use any keys file I have (I have a prod.keys file generated by Lockpick) but it doesn't specify how.
Trying to continue with the guide doesn't generate firmware files as it should nor renaming the file to keys.txt resulted in any changes.
Could anybody please give me any pointers?