The steam.desktop file currently contains:

Exec=sh -c 'STEAM_FRAME_FORCE_CLOSE=1 steam %U'

This is not compliant with the freedesktop.org Desktop Entry Specification, which explicitly states that arguments in the Exec field may be quoted using double quotes, not single quotes.

Because the command is wrapped in single quotes, desktop environments may misinterpret arguments or fail to correctly substitute field codes such as %U.

Expected behavior:
Use double quotes around arguments or, better, avoid the sh -c wrapper entirely if possible.

Suggested fix:
Replace:

Exec=sh -c 'STEAM_FRAME_FORCE_CLOSE=1 steam %U'

with either of the following spec-compliant alternatives:

Exec=sh -c "STEAM_FRAME_FORCE_CLOSE=1 steam %U"

or preferably:

Exec=env STEAM_FRAME_FORCE_CLOSE=1 steam %U```