I don't think it was ever brought up in detail here. I looked into it a while ago after realizing that she's been like this for a long time and that it was way more than just a sore throat problem. Kinda forgot to post about it though so thanks for the reminder.
Basically, Iroha was having the usual streamer throat problems throughout the fall. Too much talking/singing/etc so she cut back on her activities a bit. As she was getting better from that, the psychogenic aphonia literally hit her out of nowhere one day. She said she went to answer her doorbell for food delivery and suddenly, she just couldn't talk. No words would come out no matter how hard she tried. There were a lot of comments attributing it to Chloe graduating or working too much, but she herself said it was nothing in specific, just a bunch of stress that seemed to all hit her at once.
She did a few silent streams where she'd write out her words so she could update everyone. After talking with her doctor and management though, she decided that she wanted to continue streaming while recovering. Just small streams every so often so she doesn't stress herself out. She eventually got her voice back and began talking again around Christmas, which is when she did her comeback stream. Currently, she's at the point where she can do okay if she's reading a script or some lyrics, but having to speak on her own is where she can really struggle.
Being in the Minecraft server basically 24/7 has helped her with talking, but there are moments where it definitely gets overwhelming. I gotta shout out AZKi here because she's a damn sweetheart who's been hanging out with Gozaru all the time in Minecraft. There have been a few times where Iroha starts stuttering hard and can't finish her sentences, so AZKi steps in and helps her out. It's been a great way for her to get better without feeling pressured.
Honestly, the fact that she's talking like that in that clip you posted is a great sign of improvement from December, when she couldn't even get a sound out. Not to mention that was part of an entire 5-hour stream, which she was able to do without too many issues. Even her doctor was surprised at how fast she was recovering. It seems like it's gonna take a while longer, but I'm sure Gozaru will be talking regularly within the next few months. She's still doing dance/singing practice and will still be performing in 6th fes, which shows just how hard she's working at it. It fucking sucks but Gozaru's doing her best and deserves a bunch of love and support.
Some clips, including a wholesome one where she talks about Suisei giving her a confidence boost after her self-esteem understandably tanked from having to deal with this: