Can I find Geometry Nodes in Blender 2.91? I am new to geometry nodes and don't know whether they're in Blender 2.91 or not.
If not, can I add them into 2.91 somehow?
Geometry Nodes are new in Blender 2.92 and implemented in there by default. You cannot load them into Blender 2.91 as an Add-on.