Is it permissible to relinquish the imamate of a mosque in France due to the weak faith of the worshippers and their widespread ignorance and innovations, after they caused harm to the imam when he tried to teach them the Sunnah?

The lack of people's response to a caller's invitation is not a justification for abandoning the call to Allah. The prophets and their followers persevered in da'wah (inviting to Islam), and their concern was not the outcome, because guidance is in Allah's hands alone. The caller must convey their message and entrust the matter of guidance to Allah, as He Almighty said: {Their guidance is not incumbent upon you, but Allah guides whom He wills} [Al-Baqarah: 272], and {The Messenger is not responsible except for conveying the message} [Al-Ma'idah: 99].

The caller should possess knowledge and insight to give matters their due, so they do not condemn what does not deserve condemnation, nor remain silent about what must be condemned.