You can get mini-splits that don't have protruding wall units, but the real downside of mini-splits is indoor air quality. They don't have good filters and the

You can get mini-splits that don't have protruding wall units, but the real downside of mini-splits is indoor air quality. They don't have good filters and they basically recirculate the air in the same room. For a very tightly built house, you need to bring outside air in continuously, ideally through an energy recovering ventilator (ERV), and then you want to filter that air with a MERV 13 filter (or whatever target you want), plus you want to move and filter all the house air in general, plus you often want to control whole house humidity. Mini-splits can't do any of the above.