it’s definitely interesting! and please don’t think i’m trying to bigtime you or be condescending (and if i came off that way, i sincerely apologize), i think the tune is cool and the harmony is cool and i really just like to riff about music.
i think it’s all functional western harmony in this tune - that Ab chord is functional (presents a tritone root movement to the dominant - key is G minor, so the dominant is D, and Ab is a tritone away from D) within key as well as not shifting the key center away from G minor even temporarily. i feel like the main thing for me in a key change is the key center, or implied tonic of the harmony, is shifted somewhere else. any time that doesn’t actually happen, i’d consider it a chromatic digression or borrowed chords or passing tones, etc
