currently, the closest star to earth (proxima centauri) is approximately 4 light years away.  however, stars are not stationary, and one approaches close enough to the sun to breach the oort cloud about once every 100,000 years.  since the earth has formed, that means there have been approximately 45,000 stars that have passed by our planet https://www.universetoday.com/150815/what-are-the-best-ways-to-search-for-technosignatures/