וְלֹא־יָכֹ֣ל מֹשֶׁ֗ה לָבוֹא֙ אֶל־אֹ֣הֶל מוֹעֵ֔ד כִּֽי־שָׁכַ֥ן עָלָ֖יו הֶעָנָ֑ן וּכְב֣וֹד יְהוָ֔ה מָלֵ֖א אֶת־הַמִּשְׁכָּֽן׃
모세가 회막에 들어갈 수 없었으니 이는 구름이 회막 위에 덮이고 여호와의 영광이 성막에 충만함이었으며
Rashi
ולא יכל משה לבא אל אהל מועד AND MOSES WAS NOT ABLE TO COME INTO THE APPOINTED TENT — But another verse says, (Numbers 7:89) “And when Moses came into the appointed tent [to speak with Him then he heard the voice]”! There comes, however, a third verse and reconciles these apparently contradictory verses, for it says here כי שכן עליו הענן “For (or when) the cloud abode thereon (on the appointed tent)”. Hence you may say: so long as the cloud was upon it “he was not able to come into the appointed tent”, but as soon as the cloud disappeared he entered it and spoke with Him (Sifra, Braita d'Rabbi Yishmael 18).
Ibn Ezra
Moshe was unable to enter. Moshe was the one who placed the cover with the cherubim upon the ark in the first place. It seems likely that he was also the one who covered it with the paroches whenever they broke camp, for no one else could have gazed upon the seat of Hashem’s glory (see I Shemuel 4:4). Apparently, then, it is not that he was unable to enter the Tabernacle at all while the cloud was upon it, but only that he had to wait to be summoned, as can be seen from the first verse in Vayikra, “And He called to Moshe”.
Rashbam
ולא יכול משה לבא אל אהל מועד, at the time it was standing, assembled.