RobTop confirmed in the Geometry Dash Discord server that update 2.3 is planned to come out 6 months from when he starts working on it.
However, the catch is that RobTop said he will first work on a bugfix update for Geometry Dash 2.2 before working on 2.3. This means that 2.3 will not come out 6 months after 2.2.
So, with the Geometry Dash 2.2 release date confirmed, we think update 2.3 will come out before the end of 2024.
Assuming it takes RobTop half a year to bugfix update 2.2 after its release, we can reasonably expect update 2.3 in the summer of 2024.
Expecting it to take half a year to bugfix 2.2 is not totally unheard of when we consider the state of the Geometry Dash 2.2 private server. Regardless, 2.3 should be released no later than December 2024 assuming RobTop sticks to his word this time around.