What is this SSH syntax?

customer has a kind of proxy system for securing access. The way it access is as bellow from powershell (OpenSSH_for_Windows_8.1p1, LibreSSL 3.0.2):

ssh myAllowedUser[userTarget@xx.xxx.xxx.199]@xx.xxx.xx.198

Where is this syntax from? I've tried to replicate this, thinking if it was a ProxyJump, without success

-J [user@]host[:port]
             Connect to the target host by first making a ssh connection to the jump host and then establishing a
             TCP forwarding to the ultimate destination from there.  Multiple jump hops may be specified separated
             by comma characters.  This is a shortcut to specify a ProxyJump configuration directive.

PS C:\Users\xxxx> ssh -J myAllowedUser@xx.xxx.xx.198 userTarget@xx.xxx.xxx.199
myAllowedUser@xx.xxx.xx.198's password:
channel 0: open failed: administratively prohibited: open failed
stdio forwarding failed
kex_exchange_identification: Connection closed by remote host

I wish, when I understand what is being done, create my ssh config file as this

Host SERVER_EXAMPLE
    HostName xx.xxx.xx.199
    User myAllowedUser
    ProxyJump xx.xxx.xx.198 #Just for example here
    ServerAliveInterval 10

and then later just:

ssh SERVER_EXAMPLE

I appreciate any kind of help. Thanks

So, in the end was just a specific way that password vault use login string. That way bellow works as expected.

Host SERVER_EXAMPLE
    HostName xx.xxx.xxx.198
    User myAllowedUser[userTarget@xx.xxx.xxx.199]
    ServerAliveInterval 10

You can use it in the CLI as:

myAllowedUser%userTarget%target@xx.xxx.xx.198