Deuteronomy 16:22

As it is not for you to erect a statue, so are you not to appoint to be a governor a proud man, whom the Lord your God doth abhor.

You may not put up a monolith for idolatry, as evidenced in the qualifier which He detests. But a monolith that is not idolatrous in nature is permitted [the halakha [cf. Sifrey on this verse] is that a monolith is always a forbidden form of worship — Translator], conclusive evidence being found in the parasha of Vayyishlaḥ [Genesis 35: 14].

NEITHER SHALT THOU SET THEE UP A PILLAR — “a pillar of one stone, even for the purpose of sacrificing to Heaven upon it. WHICH THE ETERNAL THY G-D HATETH. An altar of earth and an altar of stones, Verse 22. has He commanded you to make, but He hates this [one-stone pillar] because it was an ordinance of the Canaanites [for idol-worship]. Although it was pleasing to Him at the time of the patriarchs, He hates it now, because these [Canaanites] have made it an ordinance in the worship of the idols.” This is Rashi’s language. If so, Scripture prohibited [the planting of] an asheirah [anywhere], it enjoined against planting [trees] on the Temple mount although the intent be to Heaven, and it prohibited a pillar [erected] for Heaven — both [prohibitions, against trees and against pillars,] on account of the ordinances of the Canaanites. But I have not understood this ordinance, for the Canaanites used altars as well as pillars since Scripture states, And ye shall break down their altars, and dash in pieces their pillars; for ye shall break down their altars, and dash in pieces their pillars and similarly in all places; [hence all altars should have been prohibited even for the worship of G-d]! Perhaps we may say that the Canaanites were primarily devoted to pillars, and they had no idolatrous temple without a pillar upon which to sacrifice and pour oil upon its top, similar to what is stated with reference to Baal, And they brought forth the pillars that were in the house of Baal. However, only a few of their temples also had altars upon which to sacrifice [hence Scripture did not prohibit altars built to be used for Heaven].
It appears to me that the Canaanites, who were engrossed in idolatry, used to make in all temples of their gods an altar on which to bring sacrifices, erected a large stone at the entrance of the temple for the priests to stand upon, and planted a tree outside it to point the way for those who come there. They still do so to this day. Now the Glorious Name hates and despises all their deeds and He prohibited the pillar and the asheirah. He left only the altar because it is a necessity for the offerings concerning which He commanded. They were a source of pleasure before Him — because He ordained them and His Will was done — even prior to the existence of idol-worship on earth.

ולא תקים לך מצבה, even in honour of G’d, to offer incense upon it at a time when private altars had already been banned. This prohibition went into effect after the Israelites had settled in the country and a permanent altar had been established to serve the whole nation such as in Shiloh, which served for over 300 years before the Temple of Solomon. (compare also what is written in Deut. 12,8) [Sadly, the commandment to do away with private altars was not even enforceable during the reign of Torah-observant Kings of Yehudah with the exception of King Yoshiyahu. Compare Kings II chapter 23. These altars had been used only to sacrifice to G’d, not to idols. Ed.]