Organizing sections, permissions, and content within the Class Notebook
If I recall correctly, the behavior in Teams at the end of 2023 was that OneNote channels would remember the last page accessed. The current behavior seems to be to remember the page that was selected when the channel was created. I now can have two OneNote channels which default to different pages.
I haven't found any way to change the default page on a channel (which is what I was looking for when I found this discussion). It appears that you have to create a new OneNote channel and delete the old one if you want to change the default page.