I see the Hebrew of Exodus 20:6 like this:
And you will not ascend by steps to my altar, that your nakedness be not exposed because of it.
The Hebrew word for "by steps", בְמַעֲלֹ֖ת (from מַעֲלָה: Strong's H4609 - ma`alah), only occurs this once in the Torah. In fact, the next occurrence of מַעֲלָה is not until 1 King 10:19 in regard to Solomon's great white (ivory) throne, which had six steps going up to it.
Since there is no mention of steps in the construction of the Tabernacle, this cautionary instruction was likely due to the nature of the construction of the altar and the careless practices of the priests of other nations in their worship of gods of silver and gold (Exodus 20:23).
The dimensions of the altar were:
And thou shalt make an altar of shittim wood, five cubits long, and five cubits broad; the altar shall be foursquare: and the height thereof shall be three cubits.
-- Exodus 27:1 (KJV)
Image courtesy of Altar (Bible) - Wikipedia
In modern units, a short cubit* (for small constructions) was equivalent to about 17½″ (44.5 cm), so the dimensions of the altar were 7′ 3½″ (2.225 m) long x 7′ 3½″ (2.225 m) wide x 4½′ (1.334 m) high.
Given these dimensions, it would be tempting for the priests to want to elevate themselves with steps to reach all areas upon the altar without stretching. However, Exodus 20:26 forbids them to do so. The LORD had provided instruments for the priests to be able perform their service without need of them:
And thou shalt make his pans to receive his ashes, and his shovels, and his basons, and his fleshhooks, and his firepans: all the vessels thereof thou shalt make of brass.
-- Exodus 27:3 (KJV)
The Tabernacle was a portable tent, with no mention of steps in the details of its construction. There is also no mention of steps in regard to the altar.
The details given in regard to the dimensions of the altar suggest that the priests would have found steps a convenient aid in placing offerings and in cleaning away residue, perhaps even to get up upon the altar to do so. This prohibitive commandment suggests that the LORD/Moses considered such a practice to be potentially indecorous, and not in keeping with the LORD's holiness.
* How Long Was the Original Cubit?