Source
Link to the official patch notes: check here.
Patch Notes Summary
New PVP mode - Special Arena
New Coop event - Storm Bringer
Bug fixes
Special Arena
Special Arena is now open! In Special Arena, player duels with another Commander in a best-of-three mock combat. Clear Stage 11-13 to enter the Special Arena.
Join Special Arena and win rewards such as Free Gems and Arena Exchange Vouchers. Arena Exchange Vouchers can be used to exchange rewards in Arena Shop.
The Special Arena is a 3 vs 3 team PVP match and you need to win 2 battles to win the whole thing - so the classical best out of 3.
This means that Noise alone won't be enough in this mode to carry you, especially considering that if the Special Arena looks the same as in other idle games, you will be able to adjust the order of your teams to use your weakest one against the team with Noise and focus on winning the other 2 battles.
The Special Arena will open on the 22nd of December.
New coop event
Form a team of five Commanders and challenge Boss “StormBringer” together!
Players can either team up with friends and union members or join the challenge through automatic matching. Defeat the boss and get “Broken Core” to exchange Gems and development materials in the Recycling Shop.
This time we will fight the Storm Bringer boss and for most, the name might not tell anything as you first meet the boss in Chapter 18.
Here's what he looks like:

And here's a sample video of his fight: watch it on YouTube.
Event duration: From 12:00:00, Dec 23 to 23:59:59, Dec 25, 2022 (UTC+9)
Bug fixes
As usual, no details were provided in the bug fix section and we need to wait for the maintenance to end to find out what was fixed.