Is a resident doctor in Germany considered sinful for not performing Friday prayer in congregation or at the mosque, given the nature of his work and the difficulty of reaching the mosque?

The Friday prayer is a great ritual, and abandoning it out of negligence without a valid excuse warrants a severe warning. For someone who does not meet the conditions for its obligation, such as a resident in a remote area outside of cities who cannot hear the call to prayer, or who lives a farsakh or more away, the Friday prayer is not obligatory for them, and they are not sinful for not performing it; instead, they pray it as Dhuhr. It appears from the question that the questioner is far from the place where the Friday prayer is established, and therefore it is not obligatory for them.