Basso di Aspirante:
truly, there are quite a few errors here, and I find serious deficiencies in the conduct of the parts.
i would suggest you redo it with these rules:
1 - correct notation, meaning 2 voices per staff, the upper one with stems always up, the lower one with stems always down. Otherwise, it is not clear how the parts move.
If you cannot do it this way, then it is better to have one staff for each voice.
2 - all 4 voices must always be used; in your work, sometimes the 4 voices become 3.
3 - parallel movements (see your ending) cannot last for more than 3 consecutive notes (4, but strictly at the limit...), otherwise the sense of independence of the voices, which is fundamental in these exercises, is lost.
4 - watch out for augmented 2nd intervals, which are normally forbidden. You often move from C# to Bb ....
Furthermore, if you also follow this rule, it is better:
forget about any flourishes, passing notes, etc.; concentrate on the harmony and the movement of the parts. It seems to me that you have not yet assimilated the basic rules and therefore that will be a subsequent step; right now you only risk increasing the errors.
greetings, and I hope I have given you a useful opinion and not just a "slaughtering" one