Exit from house to garden - Please provide design suggestions and photos

I also believe that removing the windowsill at the windows/doors in front of it might possibly be recommended.

You need to ensure a clean transition to the stones or terrace slabs. Drainage channels like these were installed with us.
They have proven themselves 100% so far.
No water ingress or similar has been detected.

I have regularly adjusted such outlets on "floor-to-ceiling" windows in outdoor areas using wooden terraces; a lot is possible here.

We also learned this difference just in the nick of time and anchored it as an addition in the construction contract. We are still in the finishing phase, so I can only show which variants inspired us. Regarding your current exterior windowsill and the corners: there are also clip-on ends as water drains, but I miss even those on yours. In these photos, you can clearly see the difference between floor-to-ceiling and thresholdless.