At the top edge of the walls in the bedroom, I used a rubber PVC angle profile, 4cm wide, cream color, to cover the Styrofoam insulation around these edges.
This is the angle profile: https://www.amazon.de/-/en/gp/product/B09XBLNGNQ
Then I affixed aluminum profiles for LED strips onto that angle profile and used self-taping stainless steel screws to affix the profiles onto the underlying metal bars. This provided then also support for the L-profiles - I had attached them only with glue onto the Styrofoam, and that would not last very long. , the metal bars, using self-taping metal screws. With these screws in place, that profile now sits tight at the ceiling edges.
The aluminum profiles are here: https://www.amazon.de/dp/B0C85T6YLX
They are not cheap, but are very solid and look good.
Then I used an LED strip with white resp. warm-white LEDs and attached it inside the Alu profiles. https://www.amazon.de/dp/B09NVFGQXZ
The result is as seen in the top picture of this post.
From the bed location in the bedroom the lighting looks like this:
