Yes, he was fine with worshiping with non-Catholics. There was even a procession after the debacle at Assisi, where the Catholic clergy processed alongside the members of the various false religions, from the cathedral. And remember the scandal of the pagan skull-ticklers, who were also invited to Assisi, who proceeded to sacrifice a chicken at the altar of St. Clare (though they didn't have permission). How is that even possible? The false-ecuмenism of JP2 allowed it. It's easy to forget the scandals that happened back then; Francis is hardly the first Modernist to cause great scandal.
Here's +ABL's and +de Castro Mayer's joint declaration, just as a reminder, written by he and +De Castro Mayer, to show the horrors of the Assisi scandal. It's good that the SSPX still has this on their website:
1986 joint-declaration against Assisi - District of the USA (sspx.org)
Meg, "worshiping with non-Catholics" is called
communicatio in sacris. It can be a sin, even a mortal sin in some cases. Such sins can be dispensed by a bishop if there is a good reason for the "
communicatio." Presumably, the Pope would have provided himself a "dispensation" in this case, no?
Regardless,
"Communicatio in sacris" is not the same thing as "apostasy, heresy or schism." A Pope who participates in a imprudent (even sinful) prayer meeting has not "defected from the Church." He has, at worst, committed a dispensable sin.
This was written in the 1920s with Imprimatur (
https://www.gutenberg.org/files/35354/35354-h/35354-h.html):
884. Religious communication is sinful on account of danger in the following cases:
(a) If it is a proximate and voluntary occasion of sin against faith. Examples: Sempronius goes to a non-Catholic church to hear a minister who attacks the divinity of Christ and other articles of the Creed. The purpose of Sempronius is to benefit himself as a public speaker, but he knows that his faith suffers, because he admires the orator. Balbus chooses to listen over the radio to attacks on religion and Christianity, which cause serious temptations to him.
(b) If it is a necessary occasion of sin and one does not employ sufficient precautions against it, religious communication becomes sinful. Example: Titus, a prisoner, has to listen at times to a jail chaplain, who teaches that there are errors in the Bible, that man evolved from the ape, etc. Titus feels himself drawn sympathetically to these teachings, but makes no effort to strengthen his faith.
885. Communication with unbelievers that is a remote occasion of sin, is not sinful, for “otherwise one must needs go out of this world” (I Cor., v. 9). On the contrary, reasons of justice or charity frequently make it necessary and commendable to have friendly dealings with those of other or no religious conviction. (a) Reasons of justice. It is necessary to cooperate with non-Catholic fellow-citizens in what pertains to the welfare of our common country, state, city, and neighborhood; to be just and fair in business relations with those outside the Church, etc. (b) Reasons of charity. Catholics should be courteous and kind to all (Heb., xii. 14), and be willing to assist, temporarily and spiritually, those outside the Church. Thus, St. Paul, without sacrificing principle or doctrine, made himself all things to all men, in order to gain all (I Cor., ix. 19). Indeed, the mission of the Church would suffer, if Catholics today kept aloof from all that goes on about them. The Church must teach, by example as well as precept, must be a salt, a light, a leaven, an example of the Gospel in practice; and surely this ministry will be weakened if her children aim at complete isolation and exclusivism.