I totally agree with what you saidIirc halfway has a "single Sided swingarm" i.e. no stays on the non drive side.
This usual means a stub axle, so a custom hub.
Chain tensioning on the singlespeed is an eccentric sleeve for the axle mount. more non- standard shenanigans.
As Giant did a derailleur equipped version, it should be possible to get the parts to convert to geared, but it would be a lot easier (quicker and cheaper) to just get the right bike in the first place.
Unless you want a challenge.