Is a solid house energetically much worse than a wooden house?

there is also the issue of soundproofing, which is much better in a solid house.
PS: Our neighbors in the timber frame house can no longer sleep when our lawn mower starts early at 11 a.m.

Well, let’s put it this way: just as with thermal insulation (it is somewhat more difficult to achieve excellent values in solid construction), it is the opposite with soundproofing (it is somewhat more difficult to achieve very high standards in timber frame construction). But both are doable.

there is also the issue of soundproofing, which is much better in solid construction.
PS: Our neighbors in the timber frame house can no longer sleep when our lawn mower starts early at 11 a.m.

I can achieve reasonable soundproofing in all types of construction; it depends on what and how it is built. Or do you seriously want to compare aerated concrete with KSL? And then put a properly designed timber frame construction next to it, you will be surprised.

Be very grateful to the pentagonal construction manager friend, because now you know with whom you definitely will not build.

The previous speakers have already answered in more detail.

What can already be said is that a low-energy house or even passive house standard can be achieved more cheaply with a timber frame house (not necessarily will be) than with solid construction. And that with solid construction, if extra insulation of the exterior walls is to be avoided (monolithic construction, which many prefer), an increase in the exterior wall thickness accompanies a higher standard, which can be seen as a disadvantage by some.

My wife and I had an appointment yesterday evening with a site manager who is connected to us through more than five degrees of separation. As it turned out, he works at Keitel-Haus. He strongly advised us against a house built in solid construction, with arguments like:

The "arguments" of the biased specialists (who are otherwise more salespeople than site managers) regularly differ only in wording but not in "quality." I can only agree to keep a five-corner distance from this gentleman (and perhaps to thank him for the warning not to flirt with this provider).

In general, I advise all prospective builders to decide on the construction method as follows: first, to preliminarily plan the house with a self-chosen architect, and before entering the refinement to the design planning, approach four to five providers (two timber builders, two masons, and possibly one more from any faction) openly regarding what this design (and optionally a similar design from their standard catalog) would roughly cost. From the feedback, one then derives conclusions and lets the insights flow into the further design process. Typical results of this round are:
X) one of the construction methods is (for the respective design, which can never be generalized) significantly cheaper
Y) it’s (as usually) more or less the same either way
Z) knowing early on that you need more money or have to be more modest.

PS: Our neighbors in the timber frame house can no longer sleep when our lawnmower starts early at 11 a.m.

Did you give a robotic mower a sports exhaust, or does it beep like a garbage truck when reversing?

hm.. with insulated timber panel construction you can also have good soundproofing, and just like a Kfw55 house in solid construction only consumes 55%, a house in timber panel construction consumes 55%

But it doesn't matter:

hier werden Zahlen manipuliert

Here you are being manipulated, and that is not the proper way. Build regionally with whatever you want.

Did you give a lawn mower robot a sports exhaust, or does it beep in reverse like a garbage truck?

I explicitly wrote "Mähroböterle" - the change did NOT come from me!!!