It’s starting to look like ADRIFT would be a better fit to start with.
The source code for Quest is a strange mix of VB and JavaScript with a little C# thrown in, which would make it tougher to work out how everything works from looking at that. There are also two versions of it, a desktop editor and an online version, so that would complicate matters.
It also looks like Quest 5 will be replaced by a new version that focuses more on JavaScript., although it isn’t clear when that will happen.
I haven’t looked at what extensions are available for each system, as I only have a vague idea of what I would like to create and/or what is possible these days. Most of the text based games I have played are at least twenty years old, so I have some catching up to do.
I did have a good look around the ADRIFT forums and discovered that it is possible to export an entire game file in human readable (XML) form which would help in learning how everything fits together. The manual only mentions exporting sections individually.