I've found this Dosdudes old tweet, this may be relevant:
With the new SIP disabler patch, it doesn't matter. High Sierra will think SIP is always disabled, even it is set as enabled in NVRAM.
I guess it's possible, Dosdude used this patch in Mojave too, and maybe this patch is still enabled...
EDIT: I've found on this forum (Mojave unsupported thread):
Dosdude: SIP must remain disabled at all times when running Mojave Patcher, as having it enabled will cause issues with patched system files. SIPManager.kext is designed to ensure SIP is always disabled, regardless of the NVRAM preference. You should not attempt to enable SIP when running Mojave Patcher.
SIP must remain disabled at all times when running Mojave Patcher, as having it enabled will cause issues with patched system files. SIPManager.kext is designed to ensure SIP is always disabled, regardless of the NVRAM preference. You should not attempt to enable SIP when running Mojave Patcher.
forums.macrumors.com
To be clear, I don't blame him at all, it's important that unsupported macs have SIP disabled, but now I have fully supported Macbook air.