Kirk here. The mayor of Kumamoto City and the governor of Kumamoto Prefecture have announce that KumaHaku 2023 will be held from October 7 through November 5. The Amu Hiroba (the open area in front of the Amu Plaza [the shopping mall near Kumamoto Station) and Hanabata Hiroba downtown will be the two main venues.
"KumaHaku" seems to be a portmanteau of the words "Kumamoto" and "hakurankai" (博覧会), meaning, "exhibition," but I don't think the events planned would normally warrant the word "hakurankai."
Here's the address of the official website:
https://kumahaku.kumamoto-guide.jp/
By the way, preparing this post has led me to realize that the folks who have prepared the official "Amu Plaza Kumamoto" website never got around to deciding how to distinguish the "plaza" (the entire facility) from the "square," the open space in front of it, in English. In Japanese, the facility is the "plaza" and the square is the "hiroba" but in English the ひろば is just the ひろば:
https://www.jrkumamotocity.com/en/amu
Note that no one has even bothered to make an English version of the map at the bottom of this page. If this ひろば is to be the venue for major event, I would hope that its name in English, etc. could be decided upon and placed on a proper map. :(