they related right? to D&D but no abishai or reference to 9 hells for example

Sigil is Planescape which is a different setting.

that's kind of odd

because in all other D&D games they have references

Never winter nights 2
Baldur's gate 2
if i recall BG3 have reference to Sigil

You do realize Pathfinder is D&D's rival right?

Not any more, with 5th edition being an half disaster, especially for arcane classes, most people i know still play 3.5 or switched to pathfinder.
There is a reason why none of the digital new 5th edition games allow to level after 10, or why the settings are so limited while pathfinder got 2 pretty big scope games or 3.5 got and still get so many interesting ones, seriously one glance at that 5th Ed. levelling table, or at the class specializations and i wanted to puke, and i played since 2.5

Pathfinder isn't even in the same neighborhood as D&D. Planescape is related to D&D, not Pathfinder.

Whatever the case Sigil belongs in the Planescape Setting.

Baldur's gate belongs to the Forgotten Realms setting.

There may be references/ homages in NWN and BG (though in p&p it mostly refers to mindflayers and their nautiloids, which originally belongs in the Spelljammer setting). Anyway, Pathfinder does not belong to Wizards of the Coast, NWN and BG do.

Semi off-topic:

If I may be so frank; BG3 references the BG sage but belongs to it as much as BG Dark Alliance does.

lol, I know & agree with you 100%. I was referring to the fact that their owners, Paizo & Wizards are 2 different entities.

The companies do have a history together.

Before pathfinder (and paizo) several adventures paths were published in Wizard's magazines (Dungeon) like Age of Worms and Savage Tide a number of future Paizo employee's worked on those. Would be great if those adventures were made into PC games.