Hideous HVAC unit? Are you referring to that white square on the house wall? I'd paint it to match the siding if possible or put a pot of flowers or a piece of lattice in front of it.

Yes, Can’t paint it unfortunately

Could you get a panel the same as the terrace railings and place in front of it? Your native plant choices are limited. Maybe hazel, dogwood, Viburnum opulus, V. lantana or Burnet rose?

This is the front yard? Where do people enter the house?

You'd need to make the bed on that side of the house deeper. That said, I think if you painted the vertical pipe to match your house, the white box wouldn't be that noticeable. Even if you don't get a perfect match, it will fade into the house. What are the plants to the left and the right of the box. The ones to the right look a bit overgrown, suggesting one could be transplanted.

I'd visit a local botanical garden.

Native trees and shrubs - Uppsala University

Do cars park here? They are probably more hideous than the white box. I agree that the white pipe coming from the HVAC unit is uglier than the box itself.

Someday your HVAC will need to be replaced or repaired. Make sure you leave plenty of access room around it so your new planting doesn’t get trampled by HVAC repair people.

Usually I just have a box built with 3 sides to match the deck and hide that that but lets air in and is easy to moved when needed . You can even put a top on it if you want with a big pots full of flowers but I usually try not to draw attwtion to it I do agree paint the pipe the color of the siding The deck railing looks like it needs spruce up anywahy so do both at the same time .Just like this

Since this is a country cottage I do not see the shrubs as overgrown nor the railing in need of "sprucing up". The setting is rustic, not suburban.

Why can't you paint the pipe ?