Thanks! I would like to make a second Aereven game this year, we will see how that goes.
And no, my engine isn't publicly available. I don't plan to open it to others, mostly for two reasons:
1) I don't have the time to properly document it or help users
2) It's made for me first and foremost, to support my way of working and conform to my strengths. Opening it up to others would mean changing it to also support their use-cases and workflows, which would defeat the purpose
Basically, it works for me because it isn't general-purpose like Unity/Unreal/Godot. Even a specialized engine like RPG Maker requires a ton of effort to make it suitable for a large userbase (and RPG Maker absolutely excels at this, they've been doing it for 30 years now). Trying to turn my engine into that would be a job in an of itself, and I would prefer to dedicate the time to make new games instead :)
But that's why I write those postmortem, so other people can learn and build their own engines that are similarly suited to them!