Is it obligatory to repeat Umrah or ablution due to doubt about the invalidation of ablution resulting from a feeling of wetness after performing ablution, and does this feeling necessitate repeating ablution for prayer or Umrah?

What you are feeling is obsessive doubt (waswas); the proof of this is your statement: "If I doubt my purity, I no longer feel anything." Your 'Umrah is valid, and you must cut off these obsessive doubts by turning away from them and ignoring them. If, in the future, you doubt that your ablution has been nullified or that something has exited, do not stop your prayer, do not repeat the ablution, do not pay attention to the doubt, and do not try to ascertain it. Rather, act as if nothing has exited until you achieve complete certainty that something has indeed exited.