How to permanently seal milk door

Greetings. I am a new member here. I have searched the site and the internet for ideas on this problem of sealing the milk door on my house built in the 40's without having to replace it with no luck. (see the pictures)

While I prefer not to replace it as it blends in right now and is not distracting visually. I would like to hear ideas especially from those who have solved this problem. The primary requirement is security. Both milk doors can be opened and locks on the entry door opened by reaching through. While the door is in plain site of an intersection, and traditionally our area's crime rate has been low, its a little too easy to do this. The secondary requirement is sealing / insulation.

Idea 1: I am thinking about replacing the knob with a stove bolt and putting a bracket on the other side and screwing the bracket into the frame of the milk door. Then put foam in inside for insulation and secure the inside milk door with brackets. Other ideas on securing it this way?

Idea 2: glass block the whole thing. However this will be more noticeable in terms of look of the house.

Idea 3: Brick it, but I don't have an bricks to recycle and it will be noticeable.
Others?

Thanks in advance for any ideas and suggestions?

I faced this very issue on my first house. I decided to make lemonade from the lemon by installing a plywood board from the inside and using it to mount a GFCI outlet facing outdoors. I thoroughly caulked it in place and added all the fiberglass insulation that I could on the inside. I then sealed the inside door and permanently closed it. In the end I had a new outside outlet and the milk chute was no longer an energy waster.

Thanks, that's a good idea.. How did you secure the plywood in the chute?

what about removing it and adding a family name plate there?? Then sealing it with the same type grout the brink was sealed with. On the inside just add sheet rock, or tile depending on where yours is located inside compared to the surroundings. Maybe add a decorative painting on the inside to cover it up.

just my $.02