The original author (paradoxxxzero) was not responding much for a long time, and other dev contributions kept it alive. Since there was no response from the original author, development kind of moved to its fork at
https://extensions.gnome.org/extension/3010/system-monitor-next/. Though the fork was started by "mgalgs" (who was contributing to upstream as well) as a stop gap measure, the fork gained traction and more users started using it. So, atm "mgalgs" is actively maintaining the fork. I've been using it for months without any issues.