I don't know if this is more Hebrew or if it is about biblical explication.
In Malachi 1:6, the text reads וְאִם־אֲדוֹנִ֣ים אָנִי֩ which is translated (on Sefaria and cChabad) as "If I am a master" turning adonim (which I would have thought was plural) into a singular.
The Metzudat Tziyon writes, "דרך המקרא להזכיר שם אדנות בלשון רבים וכן אדוני יוסף (בראשית ל״ט" That (my loose translation) it is the way of the biblical text to invoke the concept of master-ship in the plural, as in Bereishit 39 -- adonei yosef, the masterS of Yosef.
And Bereishit 39:20 it does read וַיִּקַּח֩ אֲדֹנֵ֨י יוֹסֵ֜ף.
This leads to two questions --
Why isn't this pluralization followed in any of the other uses of a-d-n in perek 39 (which casts doubt on the M"Tz's insight and leaves me wondering about why the plural was used in Malachi) and
How could 39:20 be constructed in biblical Hebrew to reflect a singular master in that pasuk? If pluralizing it is the only way, then it isn't significant, but required.