Is one who performs most of his prayers while sitting due to health issues, and prays at home to avoid people's embarrassment, considered sinful?

There is no objection to a sick person praying while sitting if they are unable to stand, due to the Prophet’s (peace be upon him) saying to 'Imran ibn Husayn: "Pray standing; if you are unable, then sitting; and if you are unable, then on your side." The Prophet (peace be upon him) himself prayed sitting when he fell from his horse. One should strive to pray in the mosque with the congregation and not mind people's glances, for Allah is more deserving of awe and seeking His pleasure.