Blender Python script that bevels the edges of an active object that is in OBJECT mode (see tutorial here: https://youtu.be/TFQMNcTj5Jw)

bmesh_bevel_from_object_mode_mesh.py

import bpy
import bmesh

# get a reference to the active object
mesh_obj = bpy.context.active_object

# create a new bmesh
bm = bmesh.new()

# initialize the bmesh data using the mesh data
bm.from_mesh(mesh_obj.data)

bmesh.ops.bevel(
    bm,
    geom=bm.edges,
    offset=0.2,
    segments=4,
    affect="EDGES",
    profile=0.5,
)

bm.normal_update()

# writes the bmesh data into the mesh data
bm.to_mesh(mesh_obj.data)

# [Optional] update the mesh data (helps with redrawing the mesh in the viewport)
mesh_obj.data.update()

# clean up/free memory that was allocated for the bmesh
bm.free()