Xcode is one of those products that suggest Apple has simply stopped caring about quality. It sort of works if you're lucky, but realistically it's questionably usable. And Apple just doesn't seem to care.
It's not like the company can't afford to throw some resources at it. But it... doesn't. And the process for extras like AU plugin development - not central, but a significant mini-economy in the ecosystem - used to be so much simpler than it is now.
That aside, historically my favourite accessory was Quartz Composer. It ended up being a dead end, but personally I had a blast experimenting with it and building generative animations.
It feels to me like its stuck in a hell of bad incentives. Apple seems addicted to having shiny new features to announce every year at WWDC.
A decade ago Apple would release a new, pre-release version of xcode at each WWDC with new features. The new version would be unstable, but it would become stable over the next few months with subsequent point releases.
At some point the stability work seemed to never quite get there. And now it seems like Apple is in a cycle of adding new features, launching them before they're ready, and not getting stability back to baseline before the next WWDC comes around. And next year's WWDC needs new features to be announced. XCode is now in a never ending "preview" state, where none of the features added in the last few years (since Swift) work properly. And someone at apple is acting as if what everyone wants is yet more features. (Or, more likely, the manager will only be promoted if they manage to release new stuff).
From the outside it seems like XCode is slowly drowning.
A few years ago Apple announced Snow Leopard. There was no headline feature. Apple just spent the whole year making everything more stable and faster. When they announced this it was met with thunderous applause. Snow Leopard turned out to be the best release of macos ever.
I have used it a little for modifying an app. Besides the signing/certificate stuff being super annoying and having to clear a cache (on the first build ... ????) I was actually surprised how nice it is in some places. It has issues, it is glitchy, but at least the UX concepts are kind of sound and it mostly works. This is in stark contrast to visual studio, which in my experience has no UX concept and is super glitchy and almost never works.
The only higher quality IDEs I can think of (and maybe this is sad) are the IntelliJ family and (maybe) VSCode.
It's not like the company can't afford to throw some resources at it. But it... doesn't. And the process for extras like AU plugin development - not central, but a significant mini-economy in the ecosystem - used to be so much simpler than it is now.
That aside, historically my favourite accessory was Quartz Composer. It ended up being a dead end, but personally I had a blast experimenting with it and building generative animations.