(...)
If you are unsure - ask a structural engineer.
That's it then. Only the structural engineer, who gets the complete picture on site and looks at the plans and calculations, can ultimately assess that.
I would apply a "checking aid": a dab of plaster on a spot where you have the impression that the movement is strong. This way, you can see how the situation develops.
Yes, put up this support... and then get the structural engineer... Honestly, the place is 35 years old and suddenly, after remodeling work, cracks appear. Whoever smears a dab of plaster on it and then "observes" as a complete layman... is really to blame if the place ends up collapsing in the end... No one wants to hear bad news, but it doesn't help. A professional has to take a look at it, everything else is grossly negligent.
What happened next? Has anyone with expertise looked into it yet?
It took a while, but eventually someone showed up. In the end, we were advised to do exactly what had already mentioned: simply apply some plaster and then date it immediately to see how it behaves. There is no immediate danger, but it should definitely be kept under observation.