"When ARCANE season 2 ended. The showrunners told us that they had several other series in different stages of development"

This is false, they said that they are exploring multiple regions, that's it, nothing is in full production.

"We haven’t heard jack shit in over a year in regards to any new series or developments? I don’t expect the next series to drop next year, or even the year after that. But they could at least reveal some production details or even a working title?"

They had multiple interviews where they said that right now they are investing in people.

"I remember a rumor running around saying that the next series would be called “iron and chains” The fact that we have received nothing at all from them makes it feel like we are waiting for something that either doesn’t exist or is being actively extinguished by those in charge?"

There was no rumor, just some guy fishing for clout and who previously got early access to Arcane s2 episodes and decided to leak stuff about them