Father, Son and Holy Spirit are mentioned in Matthew's baptismal creed long before any thought of, or formulation of the Trinity.
Two, possibilities as with all references throughout the NT; (1) The Father, Son and Holy Spirit in this reference do not refer to separate distinct 'persons' as the Trinity does. (2) The reference is later added like I John 5:7
From:
1 John 5:7 And Matthew 28:19 – Fabricated Trinity Verses
Eusebius (260 – 339 CE) was a Roman Christian historian and is regarded as a well learned Christian scholar. He became the Bishop of Caesarea in 314 CE. He quotes many verses in his works, and Matthew 28:19 is one of them. 17 times in his works prior to Nicaea, Eusebius quotes Matthew 28:19 as “Go and make disciples of all nations in my name” without mentioning the Trinity baptism formula.
1. George H. Gilbert Quotes Mr Conybeare and says the following on Matthew 28:19:
“There is important external evidence against the existence of this formula in manuscripts current before the time of Eusebius, and various recent writers have urge that the practice of baptism in Acts and Epistles of Paul is
utterly incompatible with the view that Jesus commanded his disciples to baptize into the name of the Father and of the Son and of the Holy Spirit (E.g., Martineau, The Seat of Authority in religion, page 515; Percy Gardener, Exploratio Evangilica, page 445; Sabatier, Religions of Authority and Religion of Spirit, page 52; Harnack, History of Dogma Volume 1, 79, note).”
.Concerning John 5:7
Brooke F. Westcott gave a long essay on 1 John 5:7 he then made the following Summary on 1 John 5:7
“…
THE WORDS ARE NOT FOUND:
(1) In any independent Greek MS (more than 180 MSS and 50 Lectionaries are quoted). Both the late MS which contain it have unquestionably been modified by the Latin Vulgate.
(2) In any independent Greek writer. The very few Greek writers who make use of the words derived their knowledge of them from the Latin (not in Ir Cl.Al Orig Did Athan Bas Greg. Naz Cyr.Al).
(3) In any Latin Father earlier than Victor Vitensis or Vigilius Tapsensis (not in Tert Cypr Hil Ambr Hier Aug Leo).(4) Not in any ancient version except the Latin; and it was not found in the Old Latin in its early form (Tert Cypr Aug), or (b) in the Vulgate as issued by Jerome (Codd. Am fuld or (c) as revised by Alcuin (Cod. Vallicell).”
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