Thanks! SQL Notebook uses .NET 6 and a custom integration with SQLite. SQLite offers a few extension points, mainly virtual tables and custom functions, and SQL Notebook takes advantage of them to provide its added functionality.
It probably represents 8-10 months of infrequent nights and weekends. I originally wrote a proof of concept in 2016 and finally picked it back up and polished it for release a couple months ago. The .NET ecosystem is in much better shape now than it was in 2016. This is all WinForms; Microsoft has done a good job of bringing support for WinForms into the latest platform. Supporting high-DPI was unpleasant but it is possible in WinForms.
You were unlucky with the Show HN post in that it didn't generate more interest. Don't let that dissuade you -- there's so much luck in what generates interest at a particular time. It really is an exceptionally useful app, one that I would have had great use for at different times over the years.