Explanatory Note – The inicial “Pope St Clement I” quotation was also sourced from the “traditionalist” Website:

www.catholictradition.org/Tradition/catholic-tradit…

«Heretical teachers pervert Scripture and try to get into Heaven with a false key, for they have formed their human assemblies later than the Catholic Church. From this previously-existing and most true Church, it is very clear that these later heresies, and others which have come into being since then, are counterfeit and novel inventionsgloria.tv/post/8S6WDtD68QpXCuJiNAbP8UFSV
Pope St. Clement I
Take for the traditionalis Website www.catholictradition.org/Tradition/catholic-tradit…

Becareful with people who take the quotes of the Saint from Wikipedia:
When I was looking for a picture of St Clement on Wikipedia I found a nude X-rated picture attributed to him on Wikipedia.

Wikipedia vs Biblehub

Wikipedia:
“Those, then, that adhere to impious words, and dictate them to others, inasmuch as they do not make a right but a perverse use of the divine words, neither themselves enter into the kingdom of heaven, nor permit those whom they have deluded to attain the truth. But not having the key of entrance, but a counterfeit key, by which they do not enter in as we enter in, through the tradition of the Lord, by drawing aside
the curtain; but bursting through the side-door, and digging clandestinely through the wall of the Church, and stepping over the truth, they constitute themselves the mystagogues of the soul of the impious. For that the human assemblies which they held were posterior to the Catholic Church requires not many words to show.”

Clement of Alexandria

Biblehub:

The Tradition of the Church Prior to that of the Heresies.

The Stromata, or Miscellanies — Clement of Alexandria

biblehub.com/…/chapter_xvii_th…
Those, then, that adhere to impious words, and dictate them to others, inasmuch as they do not make a right but a perverse use of the divine words, neither themselves enter into the kingdom of heaven, nor permit those whom they have deluded to attain the truth. But not having the key of entrance, but a false (and as the common phrase expresses it), a counterfeit key (antikleis), by which they do not enter in as we enter in, through the tradition of the Lord, by drawing aside the curtain; but bursting through the side-door, and digging clandestinely through the wall of the Church, and stepping over the truth, they constitute themselves the Mystagogues [3687] of the soul of the impious.
For that the human assemblies which they held were posterior to the Catholic Church [3688] requires not many words to show.
For the teaching of our Lord at His advent, beginning with Augustus and Tiberius, was completed in the middle of the times of Tiberius. [3689]
And that of the apostles, embracing the ministry of Paul, ends with Nero. It was later, in the times of Adrian the king, that those who invented the heresies arose; and they extended to the age of Antoninus the elder, as, for instance, Basilides, though he claims (as they boast) for his master, Glaucias, the interpreter of Peter.
Likewise they allege that Valentinus was a hearer of Theudas. [3690] And he was the pupil of Paul. For Marcion, who arose in the same age with them, lived as an old man with the younger [3691] [heretics]. And after him Simon heard for a little the preaching of Peter.
Such being the case, it is evident, from the high antiquity and perfect truth of the Church, that these later heresies, and those yet subsequent to them in time, were new inventions falsified [from the truth].
From what has been said, then, it is my opinion that the true Church, that which is really ancient, is one, and that in it those who according to God's purpose are just, are enrolled. [3692] For from the very reason that God is one, and the Lord one, that which is in the highest degree honourable is lauded in consequence of its singleness, being an imitation of the one first principle. In the nature of the One, then, is associated in a joint heritage the one Church, which they strive to cut asunder into many sects.
Therefore in substance and idea, in origin, in pre-eminence, we say that the ancient and Catholic [3693] Church is alone, collecting as it does into the unity of the one faith -- which results from the peculiar Testaments, or rather the one Testament in different times by the will of the one God, through one Lord -- those already ordained, whom God predestinated, knowing before the foundation of the world that they would be righteous.
But the pre-eminence of the Church, as the principle of union, is, in its oneness, in this surpassing all things else, and having nothing like or equal to itself. But of this afterwardsgloria.tv/post/8S6WDtD68QpXCuJiNAbP8UFSV
Of the heresies, some receive their appellation from a [person's] name, as that which is called after Valentinus, and that after Marcion, and that after Basilides, although they boast of adducing the opinion of Matthew [without truth]; for as the teaching, so also the tradition of the apostles was one. Some take their designation from a place, as the Peratici; some from a nation, as the [heresy] of the Phrygians; some from an action, as that of the Encratites; and some from peculiar dogmas, as that of the Docetæ, and that of the Hærmatites; and some from suppositions, and from individuals they have honoured, as those called Cainists, and the Ophians; and some from nefarious practices and enormities, as those of the Simonians called Entychites.
biblehub.com/…/chapter_xvii_th…