NOTATIO

The slurs are ugly whatever I do. Also it doesn't look good in general.
Perhaps I am too tired. Working 15+ hours for weeks, approaching a deadline (Friday).

Any idea how it can be solved is welcome!

How about something like this?

Three more ideas. The last one needs a left hand indicator hook but I haven’t found out how to do that in MuseScore.

Edit: I think I prefer the first idea in my post above or the last of these three.

Oh. I just realized that you put the first notes of the right hand in the lower staff and I put them in the upper one. I think that this might be easier to read and simplifies the S-shape slur solution because there is more space in the lower system.

Edit: All solutions work also with less space between the systems:

Thank you MalteM, I like your solution with kneed beam the most. I will try this, the first one with the slur outside of the stems.

EDIT: by the way, where to put the hairpins? In the middle is possible, yet, not ideally.

I actually prefer your original solution, but with the S-shaped slurs and staves closer together, as shown in the examples by MalteM. The hairpins could be carefully angled between the staves which would require that they cross through the lower staff lines. I wouldn't erase the background to allow this.

Just be careful that the endpoint of the slur doesn’t cross the ledger lines, otherwise the S-shaped solution is very good. Great point, @MalteM.
In this specific case I would put the hairpins below, since in the middle they would require too much fiddling with background erasing.

I actually tried it and agree that the hairpin is better below in this case; too hectic otherwise. So:

This looks great John!
I hadn't thought about a slanted hairpin, and that's just *the* thing!

Thanks, Neera!