Yitro says (Shmos 18,11):
"עַתָּה יָדַעְתִּי כִּי־גָדוֹל ה' מִכָּל־הָאֱלֹהִים כִּי בַדָּבָר אֲשֶׁר זָדוּ עֲלֵיהֶם׃ "
"Now I know that the LORD is greater than all gods, yes, by the result of their very schemes against [the people].”
It appears to me that this saying acknowledges the existence of other gods and Hashem's greatness over them all, just as the Egyptians did, but does not acknowledge G-d's oneness.
Also, I don't think that this can count as a true conversion.
I would like to see clarifications on this saying.