I see how to get into Notifications setting of the board, but not how to disable it for any specific person.
Someone created a board, I'm an admin of the whole Jira cloud install, so I get everything even from irrelevant projects to me.
If I try to search for how to do this, I'm only seeing replies from Atlassian saying it's not possible on next-gen projects for "simplicity"... but this is not desirable, and we don't want to lose other features of next-gen.