What is the ssh_config equivalent to this syntax involving multiple at signs

[Garbage at gmx.de]

My company uses a certain product which forces me to use a jumphost / ssh proxy.

When connecting to a server I have to type "ssh myuser at technicaluser@targethost at jumphost" everytime. I tried to simplify this by editing my ssh_config and putting this into the file:

Host targethost
  ProxyJump technicaluser at jumphost

These lines are recognized but don't work like intended because all that changes is that ssh now asks for the password of the technicaluser (for which I don't have a password due to security design).
When I run the ssh command with the three at signs this works fine, all I'm prompted for is the password of myuser.

I tried to find out more about the working solution but didn't even find a name for this. What is this syntax called and what would be the equivalent for ssh_config ?
(I want to use ssh_config because I would prefer having to type less and having a setup that works for all other applications that make use of ssh too (git, ansible, ...)

If you are interested in more details I have an open answer on Stack Exchange which contains log files (https://unix.stackexchange.com/questions/413285/hardwire-jump-host-in-ssh-config)