What should a son do with his father who mistreats and ignores him, especially after the son's financial situation has improved and he has stopped working with him?

The right of the father is great, for Allah has associated His worship with showing kindness to parents, and His gratitude with showing gratitude to them, and has made His pleasure dependent on their pleasure. Therefore, one must appease the father and treat him with gentleness, and return to working with him if that entails his satisfaction and his salary suffices for the essential needs. Otherwise, working with him is not obligatory, while continuing to show him kindness, dutifulness, and maintaining communication with him.