The battle is a standard morals off arena battle vs. Superman (DCEU version).
The second battle is one vs. the current comics version.
Said (hypothetical) D&D character is 20th level with equipment commesurate with what is standard for a 20th level PC. If that isn't enough, boost them to 25th if the system allows (or give them 5 Mythic levels if using Pathfinder). The D&D character can be any edition you are familar with in your theorycrafting (including Pathfinder) (B/X through 5th ed.) Note: The hypothetical D&D character cannot be "broken" using loopholes any reasonable GM would disallow. (No PunPun for those who are familiar). It can be a min maxed or powerful character (and probably should be) but nothing that couldn't be used at a table.
Bonus Scenario: Give Superman and the D&D character 1 week prep prior to the Battle.
Can a D&D character defeat the Man of Steel? If so, what does it take?