Are the prayers I performed previously, believing that touching the penis does not invalidate ablution based on a jurisprudential opinion, valid, or must they be repeated? And how can I do that given the impossibility of determining their number or times?

The majority of scholars hold that touching the private parts with the hand nullifies ablution (Wudu'), based on the Hadith: "Whoever touches his private parts should perform ablution." However, the Hanafis are of the opinion that it does not nullify it. The view of the majority is stronger in evidence and more cautious. The questioner should adopt this view in the future. He is not required to re-perform past prayers because he was following an opinion that did not consider it a nullifier.