Not even trinitarians agree with that.
Ellicott's Commentary for English Readers
God was manifest in the flesh.—
Here, in the most ancient authorities, the word “God” does not occur. We must, then, literally translate the Greek of the most famous and trustworthy MSS. as follows: He who was manifested in the flesh. In the later MSS., and in the great majority of the fathers who cite the passage, we certainly find Theos (“God”), as in the Received text. The substitution can be traced to no special doctrinal prejudice, but is owing, probably, to a well-meant correction of early scribes.
Cambridge Bible for Schools and Colleges
“There is no doubt that the reading ‘who’ … has the support of the ancient Greek MSS … some of which were altered to read ‘God’; the support for ‘God’ is weak … We take the reading ‘who’ unhesitatingly.”
Vincent's Word Studies
“God (Θεός) — But the correct reading is ὃς who.”
ICC (International Critical Commentary)
ὅς.] What is the antecedent? … It can scarcely be θεός, to which ἐδικαίωθη would not be suitable…”
Expositor’s Greek Testament
“If we assume that ὅς is the right reading, it is difficult to avoid the conclusion that what follows is a quotation …”
source: https://biblehub.com/commentaries/1_timothy/3-16.htm