Overview
Diablo II: Resurrected does not support 21:9 or 32:9 ultrawide at all; PCGamingWiki confirms ultrawide resolutions are pillarboxed down to a 19:9 play area, and PC Gamer reported Blizzard deliberately removed ultrawide support that existed in earlier builds because the extra horizontal view distance gave players an unfair advantage. There is no recommended fix: this is an online, Battle.net-authenticated game with anti-cheat protections, so client-side widescreen hacks are not safe to use and none is documented as working anyway.
Compatibility details
Fixes
Blizzard explicitly removed the ultrawide support that was present in pre-release builds because it broke game balance (wider view distance), and there is no safe client-side mod for a Battle.net-authenticated online game with anti-cheat, so ultrawide is permanently pillarboxed to 19:9 by design.
