There are some relatively new (in the last 25 years say) theories as to what Is 19:19 and 20, in whatever Bible translation one cares to look at, is referring to when talking about 'altar' and 'pillar', which one will not find being referenced among the notable theologians in 'Biblehub Commentaries', so I am not interested in any answers based on their theorizing, as all their comments pre date the last 25 years, when the new theorizing wasn't even plausible.
The new theories center around the Great Pyramid of Giza and the possibility that this great 'enduring'relic (possibly at least 4500 years old) is actually a portrayal of the 'Bible in Stone' and may actually mark both the first and coming 'Advents of Christ, among other time lines.
According to the scriptures, God has placed wonders in Egypt to be a sign at the return of the Lord to deliver those who call on the Lord. This altar is said to be on the border but yet in the middle. "Giza" means "border" and it is at the border of Upper and Lower Egypt. Therefore, it is also in the middle of Egypt. The Great Pyramid, the last remaining wonder of the ancient world, is located in Giza. The nature of the GP and it's complex (including the Sphinx, a would be 'pillar' possibly??), makes it the only real candidate fitting the prophecy found in Isaiah.
See also Jer 32:20a ...who has set signs and wonders in the land of Egypt...