https://www.digitec.ch/de...
e.g. Delock Thunderbolt 3 (C - C, 1.50m, 3.0)
This is not an "extension" in this sense, but simply a cable with different lengths.

If an existing cable should be "extended", it needs an intermediate piece / connector as well as another cable.
Or a cable with a m/f connector. I would simply organise a suitable cable of sufficient length.