Opti was one of the pioneers in local bus stuff. Maybe this board really early and isn’t 100% vesa compatible. And before VLB, they had some proprietary local bus motherboards.

Can you use a multimeter to check to see if the pinout is as expected? https://en.m.wikipedia.org/wiki/VESA_Local_Bus

Do you have any early VLB cards that you can try like a Tseng 4000, Mach 32 or a CL-GD5424?

The symptons suggest that it could be a bios issue. look for a newer bios.

The board has a lot of “do not touch” jumpers. would be interesting to see what they are connected to on the motherboard.

I tried with 6 graphics cards ( S3 , WDC , 7-mirage ,cirrus logic ) . Effect, always black screen 😒 ...and pc speaker sometime buzzes (not always , it depends what card I use) . Isa card Ok.
"32 bit VESA Local Bus slots (Non-functional) " . Why (Non-functional) ??

Looks like you are out of luck.

https://www.ultimateretro.net/en/motherboards/1497

Seems like they didn't quite get the VLB implimneted correctly.

Is your bios newer or older than "060692" ?

I experienced the same problem with my Jetway 402BG motherboard (https://www.ultimateretro.net/en/motherboards/10178)
I could never get that board to post with a VESA Local Bus graphics card (my S3 805 being the first one I tried).
It did, however, work fine when I installed a VESA Local Bus IDE controller card.
Mine utilsed the OPTI 495XLC chipset.