Quick answer: Godot 4 game showing the default editor icon on the Windows taskbar despite setting a custom icon? rcedit needs to patch the .exe after export - configure it in Editor Settings.
Custom .ico file referenced in the export preset. The game launches with the icon onscreen but the taskbar shows the default Godot logo.
Point Godot at rcedit
Editor Settings > Export > Windows > rcedit. Set the path to rcedit-x64.exe (download from electron/rcedit). Without it, Godot can't patch the embedded .exe icon.
Use a real .ico with multiple sizes
A 32x32 PNG renamed to .ico doesn't work. Use ImageMagick: convert icon.png -define icon:auto-resize=256,128,64,48,32,16 icon.ico.
Clear the icon cache
Windows aggressively caches icons. After re-export, delete %LOCALAPPDATA%/IconCache.db or rename the .exe.
“Windows icons live in three different places. All three need to agree.”
For Steam releases, the Steam client uses the icon embedded in the .exe for the running-game indicator. Worth getting right.