Jesus called Peter Satan. Peter was the first Pope. What does that tell us?

While I take your point, and am with you on the unbiblical nature of the papacy, are you aware that Satan is a Hebrew word that means resister, or adversary?

When found in the Bible without the definite article, thusly, שָׂטַן, it refers not to the Satan, but a satan. Even a faithful angel of God is referred to as a satan, at Numbers 22:22.

וַיִּֽחַר־אַ֣ף אֱלֹהִים֮ כִּֽי־הֹולֵ֣ךְ הוּא֒ וַיִּתְיַצֵּ֞ב מַלְאַ֧ךְ יְהוָ֛ה בַּדֶּ֖רֶךְ לְשָׂטָ֣ן לֹ֑ו וְהוּא֙ רֹכֵ֣ב עַל־אֲתֹנֹ֔ו וּשְׁנֵ֥י נְעָרָ֖יו עִמֹּֽ

But God’s anger blazed because he was going, and Jehovah’s angel stationed himself in the road to resist him. Now Balaam was riding on his donkey, and two of his attendants were with him.

When Jesus used the word as recorded at Matthew 16:23:

Ὁ δὲ στραφεὶς εἶπεν τῷ Πέτρῳ “Ὕπαγε ὀπίσω μου, Σατανᾶ· σκάνδαλον εἶ ἐμοῦ, ὅτι οὐ φρονεῖς τὰ τοῦ Θεοῦ ἀλλὰ τὰ τῶν ἀνθρώπων.”

But turning his back, he said to Peter: “Get behind me, Satan! You are a stumbling block to me, because you think, not God’s thoughts, but those of men.”

He was saying not that Peter, the faithful Apostle was Satan the Devil, but that Peter's well-intentioned efforts meant he was resisting God's will for Jesus.

JW.org