It's been three years since the Galaxy Note 9 came out. The device has already received its two major Android OS upgrades. Now that its third year of security updates has also ended, Samsung has decided that it will no longer release monthly firmware updates for the Galaxy Note 9.
That's not to say there won't be any security updates for this device going forward. The company has simply decided that there's no reason to keep this outdated device on the monthly release cycle going forward.
Galaxy Note 9 will only receive quarterly updates now
It's usual for Samsung to refresh the firmware update cycles for its devices every few months. As devices get older, they can be dropped from the monthly schedule to the quarterly. That's exactly what has happened to the Galaxy Note 9.
Samsung has dropped the Galaxy Note 9 down to the quarterly release schedule. So it will continue to receive security updates but only once every three months. This is still better than being on the bi-annual schedule. Devices on that list only receive firmware updates twice a year.
If history is any indication, the Galaxy Note 9 should be on the quarterly cycle for about a year before it gets relegated even further. It's also possible that Samsung might just drop support for the device altogether once it hits the four-year mark.