It is a slow and tedious path. But that you are on the path is progress.
The landscape that you have shared with us is beautiful, they are very beautiful photos, I understand that you found it relaxing.
I used to have nightmares daily, very vivid, disturbing. A mental trick that helped me a bit, I'm not sure if it works for you:
When I was going to sleep, I had a photo of a quiet place at hand, a landscape that I wanted very much to be in peace. In my case, it was a house next to a lake at the foot of a mountain. It can be a beach, or a place that you like.
When I went to sleep, I concentrated only on the photograph I was holding in my hand: what it would be like to be there, what the floor would feel like when walking, what the wind would be like on my face. I focused my mind as much as possible on being in that place, nothing else occupied my attention.
At first, it was difficult, but at one point I was able to dream that I was in that place. I don't know the name of the process or technique, and I don't know if it will be useful for your particular case.
But I would like to help you a little.
In my case, I also find it very difficult to concentrate and before sleep, I often struggle with my thoughts. I will try this trick, there is no harm and perhaps I will be able to divert my concentration on one thing. I have been understanding many things during my recovery process and came to know many things about myself. Sometimes it's quite difficult to accept things and unfortunately, I ended up experiencing a lot of tragedy together which I shouldn't experience like this. But as you said, my treatment is helping moving forward and I just hope eventually I will be better...