I managed to get it working!! The issue was that the Settings.toml file that comes by default with the one-click install was not compatible with the Kobo Clara 2E. Copying the Settings-sample.toml contents over to the Settings.toml (and tweaking them slightly to meet my specifications, since I was already poking on them) made it work.

I might poke on the default settings and see what the minimal tweaks are to get it working with the Clara 2E... but only after I complete my next quest, which is to make it not crash when I click Marked For Later :) (the regular tags work, though!)