The root note generated by "Realise Chord Symbol" is an octave lower

This is correct. When playing a chord symbol, it's completely normal and expected that the root would be played in the bass range. That's an essential part of how rhythm sections operate.

For a guitar neither is expected

The algorithm doesn’t differentiate based on instrument. But good solo guitarists in many styles do separate out the bass strings versus upper voices. FWIW, it depends on style but also chord voicing. Close voicings are actually not typical on guitar as well, it’s more often drop 2, simply because the tuning of the instrument pretty much requires it. Note as the tablature shows, the “expected” result is unplayable.

Both look unplayable to me.
For Guitar I'd rather expect the corresponding to

Indeed, but again, the algorithm is - by design - more generic than that. It doesn't know the specifics of guitar tuning conventions, it knows how to apply standard voicing techniques that are for the most part instrument-independent. If you choose drop 2 as your voicing, you'll often get something playable on guitar, but it won't necessarily happen to be the same exact shape used by default by beginning folk/rock guitarists.

FWIW, the algorithm is actually designed to optimize for voice leading from chord to chord more than what the basic beginning guitar shapes do. So more the sort of voicings that would be chosen by an experienced/knowledgeable professional.

As a separate feature, it could be useful to use an associated fretboard diagram rather than one of the generic algorithms.