docker build -t sshubuntu .
  docker run -d -p 2022:22 sshubuntu

In a directory where I have the attached dockerfile and a id_rsa.pub
which is the public key to my default ssh key.  

After this ssh access works with the user 'sshuser' on localhost port
2022 mapped to the server's 22.  The LSP server executable 'jdtls' is
linked to this user's $HOME/bin, or /home/sshuser/bin.

The default shell for user 'sshuser' is '/bin/bash' (though Tramp seems
to access it with '/bin/sh').  The local shell is '/bin/zsh'.

In the local machine I launch Emacs -Q sessions in slightly different
ways.  This fails:

    export REMOTE_FILE=/home/sshuser/yacy_search_server/source/net/yacy/yacy.java
    ~/Source/Emacs/emacs/src/emacs -Q                                                 \
       /ssh:sshuser@localhost#2022:$REMOTE_FILE                                       \
       --eval '(add-to-list (quote tramp-remote-path) "/home/sshuser/bin")'           \
       -f eglot

Even if it worked, I would be suboptimal.  I think I would like to avoid
the hardcoding of "/home/sshuser/bin" in my config.  This also fails.

    ~/Source/Emacs/emacs/src/emacs -Q                                                 \
       /ssh:sshuser@localhost#2022:$REMOTE_FILE                                       \
       --eval '(add-to-list (quote tramp-remote-path) "~/bin")'                       \
       -f eglot

And the following works.  Eglot is started correctly.

    ~/Source/Emacs/emacs/src/emacs -Q                                                 \
       /ssh:sshuser@localhost#2022:$REMOTE_FILE                                       \
       --eval '(add-to-list (quote tramp-remote-path) (quote tramp-own-remote-path))' \
       -f eglot

João