Is the performing of Ihram valid, and is a Fidyah obligatory due to people with disabilities wearing a medical device, socks, and trousers (sirwal) under the device during the performance of Umrah?

Your 'umrah ihram is valid, and you are not sinful for wearing the aforementioned items due to an excuse. A pilgrim in ihram commits a sin if they violate the prohibitions of ihram without an excuse. You are required to offer a single fidyah for all that you wore because these are prohibitions of the same type, and thus the fidyah is not repeated when a prohibition of the same type is repeated.