Is the 'Umrah I performed without my husband's knowledge permissible, especially since I have been at my family's home for a long time and he has not asked about me?

If Umrah is obligatory, then the husband's permission is not required, and he may not prevent her from performing it if the conditions of ability and having a mahram are met; because he is not permitted to prevent her from performing obligations. However, if the Umrah is supererogatory (voluntary), then his permission must be sought. The acceptance of Umrah is an unseen matter that rests with Allah Almighty. And if the husband is not fulfilling his marital duties, then the wife may go wherever she wishes with her family without his permission.