Doesn't matter what it looks like, problem is it changes the facade. For that you need to submit some paperwork and get it approved.

You can actually install a heat pump in most apartment buildings, as long as it's on the balcony and not visible from the street (=below waist-level). Main reason you wouldn't, is condensate output which has to be piped indoors or into a heated drain during the winter. Or you just pipe it into your balcony's rainwater drain and accept that you can't use the heatpump below 0C.

Fencing AC units is a very bad idea, as they just cause air flow problems. After all, air and refrigerant circuit exchange heat.

Obviously, people thought about this, and there are lots of fence designs that admit plenty of airflow and lots of products ready-made for this already.

Service technicians hate fences unless they are easy to remove during a service call. Honestly, esthetics is not as much concerning as the noise from compressor and condenser fan. I stayed in an AirBnb, where the outdoor unit next to the bed room, and I couldn't sleep.

Ok, you're clearly trolling it this point. Fences can open.

Sometimes it's not about the fence, it's about exerting power. Put people in charge of the decision that shouldn't be there, and you're in world of pain.

Of course not, there are numerous ways to make things look nicer.

Flowers bad, planks good?