A simple Streamlit form that provides three sets options using selectboxes limited to one choice in total.

multi_selectbox.py

import streamlit as st

blank_choice = "<----->"
options = [
    [
        blank_choice,
        "Option 1",
        "Option 2",
        "Option 3",
    ],
    [
        blank_choice,
        "Option 4",
        "Option 5",
        "Option 6",
    ],
    [
        blank_choice,
        "Option 7",
        "Option 8",
        "Option 9",
    ],
]

form = st.sidebar.form("form", clear_on_submit=True)
num_boxes = 3

with form:
    form.write("**`Dropdowns :`**")
    values = [
        st.selectbox(f"Options Set {i+1} :", options[i], index=0, key=f"set_{i}")
        for i in range(num_boxes)
    ]

    # st.write(values, values.count(blank_choice))
    form.write("")

submit = form.form_submit_button("Submit")
st.info("**Choose an option using the dropdowns in the sidebar.**")

if submit:
    if values.count(blank_choice) == num_boxes:
        st.error("**Choose an option!**")

    elif values.count(blank_choice) < (num_boxes - 1):
        st.error("**You can only tick one box!**")

    elif values.count(blank_choice) == (num_boxes - 1):
        # the 'final_choice' variable is the one you then use in subsequent code:
        final_choice = [i for i in values if i != blank_choice][-1]
        st.success(f"**Player choose option << {final_choice} >>.**")