What is the ruling on fasting on a Monday as a one-time act of solidarity with our brethren in Palestine, and is this from the Sunnah, or is it better to call people to revive all Sunan, such as fasting on Mondays and Thursdays, to achieve victory?

It is sunnah to fast on Mondays because the Prophet, peace and blessings be upon him, was diligent in doing so. However, fasting on a specific occasion has no evidence to support its legitimacy, so it should not be undertaken. Muslims must show solidarity with their brothers in Palestine and elsewhere through prayer and everything that benefits them.