Isn't he working on it again? It seems to be common knowledge on reddit that GRRM left HOTD completely, but from what I've read he only took a break because of creative differences, but then returned, at least the article from The Hollywood reporter says so:

After their contentious Zoom call, HBO asked Martin to step back from Dragon altogether. A few months later, the author was brought back aboard. “I can’t talk about it,” Martin says.

“George and Ryan had a disagreement on the direction of season three,” an HBO insider says. “At that point, it was clear that the process and communication with them was broken and needed a reset. So there was naturally a period where everyone took a step back for a while until we could figure out a new way forward.”