You need to patch the Battle.net desktop app in order to uninstall.
How to resolve issues with slow patch downloads
Standalone patches are downloaded outside of the game launcher or the Blizzard Battle.net desktop app.
Problems with patching may be resolved by disabling the read-only setting on system folders.
This error usually happens when our patch servers are down, but could be caused by local network issues as well.
Troubleshooting being unable to install or patch a Blizzard game being accessed through Game Pass