Steel beam in concrete ceiling - how to plaster?

To explain it perhaps more precisely. Our ceiling will NOT be plastered. [...] So unfortunately, applying mesh to the concrete ceiling is out of the question.

However, with a exposed concrete ceiling, the planner must have been aware that this would also mean the visibility of steel beams in between, or if he wants it differently, he should have made an execution drawing for that.

As it is in the photos, I only see the option to plaster a chamfered clean transition and then leave the steel beams visible (personally, I would find it nicer to paint them in a concrete-near gray tone).

If only the steel beams are to be plastered over, without mesh extending into the concrete surface, then a metallic mesh as plaster carrier/reinforcement with spot welding will probably have to be applied to the steel beams. Has the planner given any thought to this?

We also have a steel beam in the hallway and no plaster on the ceilings either. The plasterers filled it in with putty for us. Whether something was applied underneath, I don't know. There should be some kind of (assembly) adhesive to glue reinforcing mesh onto metal and then cover it with putty.

We also did not fill the lower area of the ceiling and only painted it, as well as a corner beam. You cannot see it. The plasterer plastered over it.

We have a similar problem, except that the beam is almost flush with the concrete ceiling and there is not much that can be filled in there anymore.

Back then, we pointed this out to the general contractor and it was agreed that steel plates would be installed underneath, but this was never done, so the beam is flush and the general contractor was chased away from the site.

In your case, I would have removed some material along the beam on the left and right so that, for example, expanded metal could be placed in between and fixed with mortar, etc., or welded to the beam (as already mentioned).

How was the problem solved?

To maybe explain it more precisely.
Our ceiling will NOT be plastered. It is also not to be suspended with drywall, because the recessed spotlights have already been planned into the concrete ceiling. So unfortunately, applying mesh on the concrete ceiling is out of the question.

Visible, bare concrete?
Or one layer of painter's fleece, then painted?

For us, it looked like this with mesh:

Such gaps are bridged with reinforcement mesh up to 20cm on the concrete, then plastered; the spot inlets pose no problem at all, as the holes are incorporated into the plaster. The reinforcement mesh can also be easily glued to steel and concrete, there's no need to make a fuss about that. With painter's fleece on the final plaster, visible crack formation is prevented in the end.