The Gidbinn in Diablo 2: Resurrected is located in a village in the Flayer Jungle, usually close to the entrance to the Flayer Dungeon, but that doesn’t necessarily make it easy to find.
After you’ve completed The Golden Bird quest and spoken to Hratli, the Blade Of The Old Religion quest will begin, and you’ll be tasked with retrieving the Gidbinn. Hratli tells you that, “As far as we know, the Gidbinn is in the possession of the Children of Light.” But it’s not; it’s in the possession of a rat man tribe deep in the Flayer Jungle.
The Flayer Jungle is beyond the Spider Forest and the Great Marsh, but the way it fits together with the Great Marsh can be really confusing. It’s possible to transition between the two without noticing, so always keep an eye on the top-right of the screen and make sure you’re in the Flayer Jungle.
Like most things in Diablo 2: Resurrected, the location of the Gidbinn is randomly generated, so you may have to search the whole of the Flayer Jungle to find it. But keep an eye out for villages, and always search them thoroughly. And if you find the entrance to the Flayer Dungeon, search there thoroughly too. The Gidbinn is usually close.
What you’re looking for is an altar that looks like a giant coconut with long spikes and two big horns. It’s labeled “The Gidbinn,” but it’s not the Gidbinn itself. Activating it will set it ablaze and summon a wave of flayers, including a unique flayer, the name of which varies. Kill that unique flayer, and it’ll drop the Gidbinn. If it doesn’t, then it could be that you killed it too far away from the Gidbinn altar, so try again and stay close this time.