Try this Regex - \d{2}/\d{2}/(\d{4}|\d{2}), though your regex will also work for all dates between 2000 to 2100 years. also many times the prefix 0 is not used in Days and Months in dates like - 1/12/2021 or 21/5/2021. In these scenarios you can change the regex to - \d{1,2}/\d{1,2}/20\d{2} or \d{1,2}/\d{1,2}/(\d{4}|\d{2})
Also I have uploaded the Uipath workflow for your understanding. You just need to change the path of your Text file.
If this solves your problem please mark it as solution.