Interesting story.
I started using Objective C in 1994 on NeXTcubes, and later NeXTstations.
For simpler, one-off projects, it was great; also great for its ability to make any existing C library or function (or even block of asm) an object that played nicely with all the rest. And every API was just another set of objects! Discovery was easy.
It wasn’t until it came to maintenance of complex codebases that it became a problem. There’s a reason things like NSurlHandler stuck around right into modern macOS — replacing objects like THAT had implications all up and down the dependency chain. Essentially, it became Apple’s equivalent of DLL Hell.
It was also the last language that I thought could be almost all things to all people; after that, I realized that specialized languages that performed really well in a single context were a much better way to go.