Hello @danarub, welcome to the community!
I have not tested the library, I’m going to take a wild guess and suppose VennDiagram is not the actual Matplotlib figure.
Using Support for Pandas charts? - #2 by andfanilo, does the following work? It looks like ax support was added in v0.6.
fig, ax = plt.subplots()
venn2(subsets=(10, 5, 2, 1), set_labels=("Group A", "Group B","G"), ax=ax)
st.pyplot(fig)
Have a nice day Streamlitin’
Fanilo 
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