Building expert for inspection and handover - recommended?

Well, I find that a bit thin – if you don't understand it yourself. So much happens between the shell construction and completion, including things you can't see in the end because they're simply covered up – many glaring defects can hide there...
As an absolute minimum, there should be an appointment after the "rough installation" when you can still see the electrical and sanitary installations. My opinion.

Due to the corona crisis, the expert came only after the rough installation was completed. In this respect, that was covered. For the underfloor heating, we also had someone who inspected the installation.

What all contributions have in common at the end of the day: It does make sense to involve a building expert in different phases. Whether this person needs to be sworn in or certified, I would doubt. There are many engineering firms that offer construction supervision with qualified personnel.

: From my own experience: Take along a recognized expert (at least for the acceptance, earlier would have been better). a) As a layperson (when buying your first house ) you have no idea anyway which details you need to pay attention to. After the acceptance, however, the burden of proof shifts>>> which is complicated, only makes sense again with experts, and is therefore also expensive. b) If, like me, you withhold the final payment because of a list of construction defects so that the general contractor finally gets moving and he then sues you: In our case, the judge really did not question a single line that the experts (from the Homeowners Protection Association) had written down; that was really astonishing. Result: We were allowed to keep half of the final payment. It was just enough for our good lawyer and the experts during the entire construction phase, but: afterwards at least all defects were meticulously and relatively perfectly remedied by the subcontractors. So it was a very good decision for us.

I just spoke with the company and they said we are no longer allowed to hire a building expert because due to Corona it will not be possible to arrange an on-site appointment. They would only meet with someone on-site at the final inspection and handover, and at these two appointments we could bring someone with us.

That is complete nonsense and I would think carefully about it if I were you. The developer is not allowed to prohibit you from hiring an external expert – also search on Google for "developer rejects building expert for acceptance". There you will find the corresponding answer from a lawyer on this topic.