When was the first house of worship/synagogue established and….and was it commanded by God…or was it something of human concoction?
As far back as Judaism goes (3300 years) it was understood that communal prayer has more power to it and most people have more concentration in an enclosed area. Also the idea of prayer/meditation in the same location has spiritual benefits and make that place “holy”. Islam and Christianity both developed later so the synagogue was the first formal house of worship for those three religions.
In the desert the Israelites had a specific “house” that was used for worship in the form of offerings. That structure was commanded by God. But my assumption is that since the concept of communal prayer exists also that its likely they had houses of communal prayer before that. We know for sure is after the exodus from Egypt the Israelites had a portable tabernacle that was the precursor to the Temples of today.
Our formal prayers in the synagogue are said to take the place of the offerings that were brought in the Tabernacle in the desert.