There’s also the max users notified per group mention setting you’d need to increase as well if you wanted to go down that route - default 100, though it can go quite high now:
Though I think people have traditionally preferred creating an #announcements style category or tag and setting that as ‘Watching First Post’ in either default categories watching first post or default tags watching first post so people will get a notification of any topics/announcements that way. This is considered a softer approach and allows people to ‘opt out’ if they want to.