Ultra Widescreen resolutions are not supported for Warcraft III. Currently, there are no plans to have this resolution to be supported in the future.
While it is not supported, a few members here have provided some workarounds with some caveats, but it may be worth checking out a few workarounds provided by our community members. Thank you for those who shared!
If you do have feedback or suggestions, please post on the General forums. The technical support forums isn’t the appropriate place to provide feedback as it’s intended for troubleshooting technical issues.