When the tabernacle was finished, what covered the Tent of Meeting as God's glory filled it?

Answer: A cloud

The cloud covered the Tent of Meeting and the glory of the Lord filled the tabernacle, so Moses could not enter.

“Then the cloud covered the Tent of Meeting, and the glory of the LORD filled the tabernacle. Moses was unable to enter the Tent of Meeting because the cloud had settled on it, and the glory of the LORD filled the tabernacle.”— Exodus 40:34-35 (BSB)