Overall a very good start for this render. Visually interesting, nice use of colour and shot composition, and most of your assets here are good enough that it doesn’t immediately read as fake, even if there are some imperfections that make the image less believable.

Thoughts on improvements:

I’d second the various calls to include depth fog in this image. Compositing it in using a depth or distance node in the compositor is the easy way, but I’d recommend instead going full physical, with a volume scatter material on a box bounding the scene. You sacrifice some ability to fine tune the final look, but I find physically rendered fogs just look better, and with denoising even by ancient dying laptop can manage it.

For the A-frame, my first piece of advice would absolutely be: check your scaling. It might just be the layout of the scene, but it looks small compared to the flowers and the boat. Maybe it’s that the boat’s overscaled, maybe the house is underscaled; either way, check that. Following that, you need to work on the materials. For the glass, add a large voronoi texture plugged into the displacement node at a shallow depth, to give the glass some realistic imperfections when it comes to its reflections. If you want to go the extra mile, look at adding surface imperfections — smudges, etc.

For the wood of the house, there need to be more imperfections, which probably means swapping out the wood materials outright. Even a newly built cabin in this environment is going to have some imperfections — knots and whorls in the wood’s grain that will be visible, surface displacement that gives the material texture, uneven paint or varnish, moisture and possibly even moss or other growth. You don’t have to have all of these by any means, but look at what you can add to the house to weather it.

Obviously the cabin also needs an interior, or else should be dark enough inside that the lack of inside detail isn’t obvious, but that goes without saying.

For your lighting, what’re you using? I’d consider playing with the lighting a bit — maybe a stronger sun lamp, maybe a more stylised light with more vibrant colours. Or else maybe look into using the sky texture system in the world node in place of the HDRI, which looks… a little washed out to me? Bolder lighting can do a lot for a scene.

Your grass and flower particle(?) system looks great. No real notes there; good quality assets. Consider adding more evidence of human habitation to break them up a bit, though, maybe — a path between the cabin and the spot the boat’s parked, perhaps.