How can one seek forgiveness for a paternal uncle who severed ties of kinship and died without offspring, and is it permissible to perform Umrah on his behalf?

Religion encourages maintaining kinship ties and forbids severing them. Allah Almighty associated the severing of kinship with corruption on earth in His saying: "So would you perhaps, if you turned away, cause corruption on earth and sever your [ties of] kinship?" The Prophet, peace and blessings be upon him, clarified that kinship seeks refuge with Allah from being severed, and that Allah connects with those who maintain it and cuts off those who sever it. The true maintainer of kinship is one who connects with his relatives even if they have cut him off. If you fell short in maintaining ties with your uncle while you were able, then you must repent. You should also frequently supplicate for his forgiveness and mercy after his death, as this is one of the best forms of maintaining ties.