Mark 1:1 no longer says Jesus was the Son of God.
Mark’s opening line now says merely: ‘The beginning of the good news of Jesus Christ.’
A footnote in the NRSVUE to this opening verse says ‘Other ancient authorities add Son of God.’ In the previous edition the NRSV rendered Mark 1:1 as: ‘The beginning of the gospel of Jesus Christ, [the Son of God].’ Then the footnote said ‘Other ancient authorities lack the Son of God.’
The Jewish Annotated New Testament (2011), also based on NRSV, renders Mark 1:1 with the phrase ‘Son of God’, but without any brackets, simply as: ‘The beginning of the good news of Jesus Christ, the Son of God,’ noting that ‘Other ancient authorities lack the Son of God.’ (p57)
The Oxford Annotated Bible (2010), based on NRSV, renders it the same as the above without brackets and with a footnote to say ‘Other ancient authorities lack the Son of God.’ See p.1792.
The Comprehensive New Testament by the Klontz brothers (2008), based on the NRSV translation of the Greek New Testament text of the 27th edition of the Nestle-Aland, sets out the manuscript traditions and also has the phrase [the Son of God] in hard brackets. They say it is found in Alexandrian and Byzantine MSS traditions, but is omitted from Minor MSS traditions. (p.52) They do not give any indication of whether it is attested to in earlier or later MSS.
The fifth edition of The Greek New Testament (2014), based on the 28th edition of Nestle-Aland Novum Testamentum Graece, also has the verse with the phrase υἱοῦ θεοῦ in hard brackets, to indicate that it is disputed, as follows: Ἀρχὴ τοῦ εὐαγγελίου Ἰησοῦ Χριστοῦ [υἱοῦ θεοῦ].
The discovery of P. Oxy. 76 5073 in 2011, which has Mark 1:1-2 without it. It has been dated as early as late 3rd century while all the other early manuscripts are dated to 4th century the earliest. Also, Codex Sinaiticus only has it in superscript.
https://www.worldcat.org/title/oxyrhynchus-papyri/oclc/855777953
Below is the wording on this particular amulet found in Egypt, it is dated to the 3rd/4th century and does not include the phrase Son of God:
ἀνάγνωθι τὴν ἀρχὴν τοῦ εὐαγγελίου καὶ ἴδε.
Ἀρχὴ τοῦ εὐαγγελίου Ἰη(σο)ῦ τοῦ Χρ(ιστο)ῦ.
ὡς γέγραπται ἐν Ἠσαϊᾳ τῷ προφήτῃ
ἰδοὺ ἀποστέλλω τὸν ἄγγελόν μου
πρὸ προσώπου σου, ὃς κατασκευάσει
The five lines are translated as:
Know well the beginning of the gospel and see,
The beginning of the gospel of Jesus the Christ.
As it is written in Isaiah the prophet:
“See, I send my angel
before your face, who will prepare.”
https://babel.hathitrust.org/cgi/pt?id=njp.32101074938968&view=1up&seq=96&skin=2021