I am a mod of r/portland. We use a 3rd party chat app and other web applications.
We also have custom tuned automod and other software to help out. A lot of the need for these services is because Reddit has failed to provide necessary tools in a timely way forever.
For example, our sub has been under brigade since the national news began focusing on it this past administration. The company did nothing for us, not even words of support.
The company has spurned volunteer mods long enough they have got whatever’s coming to them. It isn’t just an API people are upset about.
Anyway, the software tools for collaboration matter in moderation, but even more so it is a huge amount of work to keep a sub from going off the rails.
I’ve seen comments of people thinking it’s mostly power stuff and there are elements of that at play. But it doesn’t work day to day. Big subs that aren’t moderated constantly fall on hard times.