The GPIO page needs to be overhauled to account for the new ABI that's using character devices.
GPIO SYSFS has been marked obsolete in 2015 and I can't get it to work with the scripts provided on the wiki.
I just added an info box to the GPIO page in the wiki so other people won't waste their time like me ^^. https://openwrt.org/docs/techref/hardware/port.gpio#software
But someone more knowledgeable should take a look and overhaul the page, I guess.
I won't be the last person that's new to the project and is trying to add new LEDs to a dts, that were missing before. The current wiki page is/was frustrating because it didn't work at all.
Here's a great article on the topic: