The Samsung Galaxy S8 and S8+ celebrated their three-year birthdays a while ago, and Samsung has now relegated them to its quarterly update list, with support expected to end completely in a year. The S8 Active and Galaxy Note 8, however, remain on the monthly update list.
https://www.notebookcheck.net/The-Samsung-Galaxy-S8-and-S8-have-now-been-relegated-to-quarterly-security-updates.463691.0.html