This port will be removed on 2020-12-31 if not fixed
lang/spidermonkey68's only reason of existence is a never committed dupdate of polkit to 0.117 (ovecome by 0.118).
So I don't see any reason to invest time in making it work in a python3 world.
A commit references this bug:
Date: Thu Sep 24 19:25:47 UTC 2020
New revision: 549941
lang/spidermonkey68: mark deprecated
lang/spidermonkey68 was added to be able to update polkit to 0.117.
Which has in the meantime been updated to 0.118 which builds with a
python3 using spidermonkey version.
Reported by: swills