If you read the complete verse of Leviticus 11:21, the legs of a kosher flying insect הָע֔וֹף are 6 [legs] = אַרְבַּ֑ע Arba 4 [legs] + 2 Kra'ayim כְרָעַ֨יִם֙ Jointed [legs] above.
In Hebrew, the phrase " הָע֔וֹף הַהֹלֵ֖ךְ עַל־אַרְבַּ֑ע " means "insect that walks on four [legs]" in English. - Notice the additional 2 Kra'ayim כְרָעַ֨יִם֙ Jointed [legs] above the regular four legs for hopping.
Leviticus / Vayikra 11:21 [MT]
"However, among all the flying insects that walk on four [legs], you may eat [from] those that have jointed [leg like] extensions above its [regular] legs, with which they hop on the ground." ( אַ֤ךְ אֶת־זֶה֙ תֹּֽאכְל֔וּ מִכֹּל֙ שֶׁ֣רֶץ הָע֔וֹף הַֽהֹלֵ֖ךְ עַל־אַרְבַּ֑ע אֲשֶׁר־ל֤וֹ (כתיב אשׁר־לא) כְרָעַ֨יִם֙ מִמַּ֣עַל לְרַגְלָ֔יו לְנַתֵּ֥ר בָּהֵ֖ן עַל־הָאָֽרֶץ )