If you want to simplify the joinery simply cut it per your picture and use ceramic coated Torx head, or timber tite screws to hold it all together. Not sure if the Torx head screws are long enough to secure the horizontal beam to the post but shorter ones work well on the cross brace. Drill countersink holes in the brace so the head does not protrude beyond the face of the brace. Low tech use galvi lag bolts but make sure they are compatible with pressure treated wood .
Almost all the force will be downward so the fasteners/joinery is not under much stress.