How do I read midi / musicxml files in music21 for solo piano where there can be multiple notes in a voice simultaneously?

I have written a python script to process midi files with music21 and write again a midi file. This works if the solo piano is "simple" in the sense, that there are not multiple pitches / notes played simultaneously in a voice.

https://github.com/githubuser1983/algorithmic_python_music/blob/main/12RootOf2.py

The relevant part from above is:

def parseMidi(fp,part=0):
    import os
    from music21 import converter
    print(fp)
    score = converter.parse(fp,quantizePost=True)
    print(list(score.elements[0].notesAndRests))
    #print([e.partAbbreviation for e in score.elements][0])
    from music21 import chord
    durs = []
    ll0 = []
    vols = []
    isPauses = []
    for p in score.elements[part].notesAndRests:
        #print(p)
        if type(p)==chord.Chord:
            pitches = median([e.pitch.midi-21 for e in p]) # todo: think about chords
            vol = median([e.volume.velocity for e in p])
            dur = float(p.duration.quarterLength)
            #print(pitches)
            ll0.append(pitches)
            isPause = False
        elif (p.name=="rest"):
            pitches = 89
            vol = 1
            dur = float(p.duration.quarterLength)
            ll0.append(pitches)
            isPause = True
        else:
            pitches = p.pitch.midi-21
            vol = p.volume.velocity
            dur = float(p.duration.quarterLength)
            ll0.append(pitches)
            isPause =  False
        durs.append(dur/(12*4.0))
        vols.append(vol*1.0/127.0)
        isPauses.append(isPause)
            #print(p.name,p.octave,p.duration.quarterLength)
    #print(dir(score)) 
    #print(ll0)
    #print(durs)
    return ll0,durs,vols,isPauses

Another option would be to to read musicxml instead of midi. What I need for the algorithm to work, is a list of note(s) = (pitch, duration, volume, isPause) for each voice.

Thanks for your help.