Szczepan Bialek wrote:
"Normally there is a tuned circuit at the input, which consists of a
coil and capacitor in parallel. The DC flows through the coil.

At the output there either is a high-impedance magnetic headphone,
which conducts DC through its coil, or a crystal headphone with a
resistor in parallel for the DC path."

Next the DC flows into "ground":

NO NO NO NO NO!!!!

The DC flows in a circle inside the receiver!!!

When you see the schematic diagram of a working crystal receiver,
you can make a trip trough the diode, through other components in
the receiver, all conducting DC, back to the the point where you
started at the diode.

This path must exist and this is where the DC flows.

The path is the ground:

Can't you read?
Or are you even dumber than I already think?

The path is not to the ground. It is a circle inside the receiver.

When there is no such path, a DC voltage equal to the peak value
of the HF voltage will develop across the diode, the diode will
no longer conduct, and there is no more rectification. Hence the
receiver will not work.

This is not related to "ground". There must be HF voltage at
the input of the receiver, but it is not important if it is between
a monopole antenna and ground or between the poles of a dipole.

Each voltage disappear (leakage) with the time. That before diode and that
after. The leakage is always and everywhere.
The leakage is surface and humidity dependent.

Only a bad designer will design equipment that requires leakage to
operate. Of course there will be some bad schematics of crystal receivers
around, where there is no obvious DC path around the diode, and maybe
sometimes (depending on construction details) one may be able to hear
some sound, but it is NOT the way it should be done and it is NOT the
explanation of the workings of the receiver.
Except maybe to someone in 1900, who did not understand it fully.

You can even make a crystal receiver with a ferrite rod as an
antenna, which will operate without any ground.

Leakage do the work.

I think leakage has done the work to your brain. Leakage from the
beer bottle, that is.