John Gill Commentary Deuteronomy 4:11

"And ye came near and stood under the mountain; and the mountain burned with fire unto the heart of heaven, with darkness, cloud, and thick darkness." — Deuteronomy 4:11 (ASV)

And you came near and stood under the mountain
At the foot of it, in the lower part of the mountain, as the Targum of Jonathan, and agrees with (Exodus 19:17)

and the mountain burnt with fire to the midst of heaven ;
the flame and smoke went up into the middle of the air: with darkness, clouds, and thick darkness; which thick darkness was occasioned partly by the smoke, which went up like the smoke of a furnace, and partly by the thick clouds, which were on the mount, and covered the face of the heavens, which were black and tempestuous with them; the Septuagint renders it a "tempest", (Exodus 19:18) (Hebrews 12:18) , which denotes the obscurity of the law, and the terrors it works in the minds of men.