Is concealing good deeds out of fear of people seeing them considered sincerity or polytheism?

It is wrong to stop doing good deeds out of fear of people. A Muslim should strive to be sincere and not abandon good deeds for fear of showing off, for Satan encourages abandoning good deeds through this door. The remedy for this is for a Muslim to begin his work sincerely, and if Satan whispers to him, he should seek refuge in Allah from polytheism (shirk) and showing off (riya') and continue his work. It has been narrated from the Prophet, peace and blessings be upon him, a supplication to guard against hidden polytheism: "O Allah, we seek refuge in You from associating anything with You knowingly, and we seek Your forgiveness for what we do not know." Al-Fudayl ibn Iyad said: "Abandoning action for the sake of people is showing off (riya'), and acting for the sake of people is polytheism (shirk). Sincerity is that Allah protects you from both." Al-Izz ibn Abd al-Salam explained that if Satan cannot tempt a servant to abandon obedience, he makes the servant imagine that he is showing off, and that abandoning obedience with showing off is better than performing it with it. This is a lie from Satan, as abandoning a good deed out of fear of showing off is not sincerity.