I’m still using IDE 1.65 on High Sierra and haven’t used an extension project since 2015. But I recall that even back then I had trouble making the Test button to appear and Examples menu to populate in a project of my own. This would be independent of any actual break that may have occurred since.
When I looked for help, Zarf suggested there could be really subtle compiler / IDE disagreements about formatting (technically, bugs) that could be stopping the IDE recognising the source as an extension project. In my case, he was right. I had an indent out of place or somewhere the IDE didn’t like, and once I fixed that it started working. (6M62 - how to do something with an extensions project? - #2 by zarf)
Having said all that, today I tested the ‘Create from an installed extension’ option with Emily Short’s Introductions, and it instantly made a working extensions project. So if you can’t do that with this extension, then maybe Petter’s right about it having broken.
-Wade