Recreate the crash and check the logs. Bottles should be writing logs, as well as the OS.
My guess is that Steam installs some extra dependencies which are also used by Bottles.
I’m not a Gentoo expert in the slightest, so I can’t really comment on how to find out what extras your package manager installs.
I just tested on mine:
Right click game in steam, add shortcut to desktop double-click shortcut, game runs.
I checked the shortcut to see what the command is (right-click, properties):
steam steam://rungameid/648800
Is that what you have? The only thing I can think of is that steam isn’t in your path, ie when you double click the shortcut it tries to run ‘steam’ but then can’t find it.
If you open a terminal and type:
which steam
what’s your output? You should have something like /usr/bin/steam
Hmm… have a read, there might be something to help you here:
https://docs.usebottles.com/utilities/logs-and-debugger