Desktop file for aseprite from Steam, make sure to replace USERNAME with your username. Place on /usr/share/applications/ or ~/.local/share/applications/

Aseprite.desktop

[Desktop Entry]
Type=Application
Encoding=UTF-8
Name=Aseprite
GenericName=Sprite Editor
Comment=Animated sprite editor & pixel art tool
Icon=/home/USERNAME/.steam/steam/steamapps/common/Aseprite/data/icons/ase64.png
Categories=Graphics;2DGraphics;RasterGraphics;
Exec=/home/USERNAME/.steam/steam/steamapps/common/Aseprite/aseprite %U
TryExec=/home/USERNAME/.steam/steam/steamapps/common/Aseprite/aseprite
Terminal=false
StartupNotify=false
StartupWMClass=allegro
MimeType=image/bmp;image/gif;image/jpeg;image/png;image/x-pcx;image/x-tga;image/vnd.microsoft.icon;video/x-flic;image/webp;image/x-aseprite;