If OSD is not locked, try to raise manually brightness on OSD. AFAIK Benq has no public SDK like Dell or HP for their widegamut.. so nothing can be done to fix your HW cal even if you have programming skills.
If you cannot make HW cal to work, move to user / custom OSD presets and calibrate grey in GPU with DIsplayCAL.
If you need some kind of sRGB/Rec709 emulation, check i it is available on OSD fro user/custom preset or check if there is some kind of 6 axis control (use HCFR or some MS paint patches + Argyll commandline spotread).
This reply was modified 6 days, 6 hours ago by Vincent.