"A letter from a concerned priest"
One person argues it is an idol, and another argues it is not. That is an opinion evaluating circumstances. But the irrefutable argument against the claim that Francis committed idolatry is not opinion. Vatican I taught, as the culmination of many centuries of teachings from Popes, Saints, Doctors, and Councils, that every Pope has the charism of truth and of never failing faith. Therefore, no Pope can ever be guilty of heresy or apostasy or idolatry or any other grave failing of faith. This is dogma under the ordinary universal magisterium and was taught by Constantinople III and Vatican I.
Sadly, I suspect you will still be writing on this topic in around 30 years time, as it is the same debate as the so-called blasphemous inter-religious gathering in Assisi in 1986. Rather than looking for that which unites us, there are those who look to preserve a particular tradition or understanding of what it means to be Catholic. Unsurprisingly, this lens just happens to accord and align with their cultural heritage.