likely pilot-error (Narrator: it usually is!) but searched this forum and the github tracker and crickets/nothin' -

./itch-setup: symbol lookup error: ./itch-setup: undefined symbol: gtk_action_bar_get_type

this is on an aged mint17/trusty system, libgtk3/libgtkmm3 present, even now added the i386 versions just in case. tried running it thru gdb, but no helpful info from that. memory and disk are not a constraint.

egray@tucson ~ $ uname -a
Linux tucson 4.4.0-148-generic #174~14.04.1-Ubuntu SMP Thu May 9 08:17:37 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
egray@tucson ~ $ aptitude show libgtk-3-0
Version: 3.10.8~8+qiana

vs. a slightly-less-ancient mint19/bionic machine where the itchio application installed and runs just fine -

egray@mahakala ~ $ uname -a
Linux mahakala 5.3.0-59-generic #53~18.04.1-Ubuntu SMP Thu Jun 4 14:58:26 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
egray@mahakala ~ $ aptitude show libgtk-3-0
Version: 3.22.30-1ubuntu4