Display a 2d button gizmo in the 3dview window for an addon UI

gizmo_button.py

from bpy.types import (
    GizmoGroup
)
import bpy
bl_info = {
    "name": "POC buttons",
    "description": "POC 2D BUTTON script refactored from GP Animator Desk addon",
    "author": "Anthony Aragues, P.Świda",
    "version": (0, 0, 1),
    "blender": (3, 4, 0),
    "location": "3d window",
    "wiki_url": "",
    "tracker_url": "",
    "category": "UI"
}


class AD_3DVIEW_UI_Buttons(GizmoGroup):
    bl_idname = "GP Animator Desk UI Buttons"
    bl_label = "GP Animator Desk UI Buttons"
    bl_space_type = 'VIEW_3D'
    bl_region_type = 'WINDOW'
    bl_options = {'PERSISTENT', 'SCALE'}

    @classmethod
    def poll(cls, context):
        # modify this to whatever conditions you need for showing this gizmo group
        return True

    def draw_prepare(self, context):
        # set the x and y for the gizmo, by default starting from bottom left == the center of the gizmo
        self.button_gizmo.matrix_basis[0][3] = context.region.width/2
        self.button_gizmo.matrix_basis[1][3] = 40
        self.button_gizmo.color = (1, 0, 0)
        self.button_gizmo.color_highlight = self.button_gizmo.color
        self.button_gizmo.alpha = 1
        return

    def setup(self, context):
        # array not necessary, but might be useful if setting up several
        # a collection might be better where each gizmo props are read and set. But his is fine for POC to understand
        gizmos = []

        gizmos.append(self.gizmos.new("GIZMO_GT_button_2d"))
        gizmos[0].icon = 'BLENDER'
        gizmos[0].draw_options = {'BACKDROP', 'OUTLINE'}
        gizmos[0].alpha = 0.8
        gizmos[0].color = 0, 0, 0
        gizmos[0].color_highlight = 0.0, 0.0, 0.0
        gizmos[0].alpha_highlight = 0.3
        gizmos[0].scale_basis = (80 * 0.35) / 1.8
        gizmos[0].show_drag = False

        self.button_gizmo = gizmos[0]


def register():
    bpy.utils.register_class(AD_3DVIEW_UI_Buttons)


def unregister():
    bpy.utils.unregister_class(AD_3DVIEW_UI_Buttons)