Does my donation to those in need of assistance, while also having an interest in improving work relations with the authorities responsible for them, constitute showing off (riya') or diminish the value of my good deeds, even though I intend this act for the sake of Allah?

Whoever wishes to give charity should prioritize the needy over others, for charity given to the distressed is multiplied many times over. Similarly, one should prioritize whatever brings benefit to the religion of Allah Almighty. If the giving is more obedient to Allah and more beneficial to the religion of Allah, then it is more deserving. If the giver considers the most needy in their charity, they will receive the full reward of the charity, and their reward will not be diminished by any worldly benefit they did not intend.

As for working for the sake of worldly gain, if the servant's entire intention is for this purpose and not for the sake of Allah and the Hereafter, then they will have no share in the Hereafter. However, if one works for the sake of Allah and for worldly gain, and both intentions are equal or close, then their faith, monotheism, and sincerity are deficient. But if one works solely for Allah and is completely sincere in their work, yet receives a specific wage for their work to help them in their work and religious duties, then their receiving of it does not harm their faith and monotheism.