So my advice is to learn about manuscripts.
It is when we consider the mss, that the position taken against the KJB, is seen as being erroneous.
Romans 16:24
Rom 16:24 The grace of our Lord Jesus Christ be with you all. Amen.
The NIV and the NWT follow the same pattern:
https://www.biblegateway.com/passage/?search=Romans+16:24&version=NIV
https://www.jw.org/en/library/bible/study-bible/books/romans/16/#v45016024
The words do not occur in the following corrupted texts:
Aleph (Sinaiticus), B (Vaticanus), A (Alexandrinus), C
Here is the vast extant literature which has the text in it:
"... D, E, F, (G*), L,
Psi
Cursives: MAJORITY (including 88, 181, 326, 330, 451, 614, 629, (630), 1241, 1877, 1881, 1984, 1985, 2492, 2495.)
Old Latin: ar, d, dem, (e*), (f*), (g*), gig, (x*); Vulgate: Clementine, tol, harl, demid;
Syriac: Harclean
(Gothic)
Chrysostom, Constantinople, 407.
Euthalius, Sulci, 458.
Theodoret, Cyrus, 466. ..." - When The KJV Departs From The "Majority" Text of Hodge & Farstad, cited by the Corrupt NKJV, by Jack Moorman, page 67
Support for the Doxology being placed at the end of Romans 16:24.
"... P61,
Aleph (Sinaiticus), B (Vaticanus), C, D, D-abs,
5, 81, 88, 256, 263, 296, 365, 436, 623, 630, 1319, 1739, 1838, 1962, 2127, 2464, others.
Old Latin: a, ar, b, d, e, f, gig, x, 2 Vulgate: am, fuld, demid, harl, tol, others.
Syriac: Pes.hitta
Coptic: Sahadic, Bohairic
Ethiopic.
Clement, Alexandria, 215.
Origen, Alexandria, Caesarea, Greek and Latin, 254.
Ambrosiaster, Latin, 354.
... The Latin mss. dol Origen, in his commentary on the Epistle claimed that confusion in the Greek mss. can be traced to the influential heretic, Marcion, who removed chapters 15 and 16 from his edition of Romans. ..." - When The KJV Departs From The "Majority" Text of Hodge & Farstad, cited by the Corrupt NKJV, by Jack Moorman, page 67
Additionally:
"...
Romans 16:24 is found in the Majority of all remaining manuscripts including D, L, Psi, and it is found in the Old Latin copies ar, d, f, g, mon and o. It is also found in the Syriac Harclean and Peshitta as well as the Slavonic, Armenian, Ethiopic, Coptic Boharic and Georgian ancient versions, though some place it at the end of the chapter. ..." -
https://brandplucked.webs.com/romans1624.htm