Interpreting harmony

I'm writing a little piece for strings and I don't know how to play a measure myself.
In the end, I don't care either, I know that it comes from voice conduction, but well, let's guess what it could be...
It is bar 4 (in blue).
The piece is in D minor. Although it starts in G minor. So Gm - Dm - ¿¿??  F.....
Since the resulting chord in that measure (after what I consider some appoggiaturas) contains Gb - Ab - Cb.... it could be called Gbsus (with its 2 = Ab and with its4 = Cb). Somehow it links to the following chord by descending semitone (F).

On 10/27/2024 at 11:10 AM, Luis Hernández said:

The piece is in D minor. Although it starts in G minor. So Gm - Dm - ¿¿??  F.....
Since the resulting chord in that measure (after what I consider some appoggiaturas) contains Gb - Ab - Cb.... it could be called Gbsus (with its 2 = Ab and with its4 = Cb). Somehow it links to the following chord by descending semitone (F).

I think the chord is kinda functioning as a French 6th in Bb major.  Despite the fact that it's missing an E on top to create the necessary augmented 6th, the function of the tritone substitution is still there since there is a Bb in the Violas.  And the slip into the suspended 4th (Cb) and the addition of the 2nd (Ab) is a very individual and unique harmonic characteristic that makes sense with the voice leading between the two chords.