"Zack Snyder is addressing the horrible CGI removal of Henry Cavill's Superman mustache that made its way into Joss Whedon's Justice League cut." https://screenrant.com/justice-league-zack-snyder-superman-cavill-cgi-mustache
https://screenrant.com/justice-league-superman-mustache-fix-how
https://www.studiobinder.com/blog/what-is-post-production CGI and other effects are so good now that essentially any mistake can be corrected in post-production. Yet, sometimes various problems remain in the final product.
If you haven't been to CC, you don't know what your are missing. https://www.youtube.com/c/corridorcrew/videos
https://thedigitallabyrinth.blogspot.com/search?q=CGI
https://thedigitallabyrinth.blogspot.com/search?q=Justice+League+Snyder+Cut