Hi, I use Trinity on Arch Linux. I didn't use a display manager, but
rather started Trinity and I3 through .xinitrc script (I don't know if
it is relevant).

After installing Trinity, some of GTK apps (Midori, dwb) failed to
start in I3, with similar message:
"Could not find mime type application/octet-stream" and segfaut. Didn't
test in Trinity.

First quick fix was to set an environment variable
GSETTINGS_SCHEMA_DIR=/usr/share/glib-2.0/schemas
but some other apps (SpaceFM) still segfaulted after many error
messages. Then I disabled /etc/profile.d/trinity.sh and started it only
when starting Trinity, which solved my problem.