Samsung no longer supports Galaxy S8
Samsung has finally ended support for most of the Galaxy S8 series. The exceptions are the Galaxy S8 Active and Galaxy S8 Lite, which came out months after the main S8 phones were released. It isn't surprising that Samsung halted support for these 2017 flagships. As Engadget pointed out, even Google doesn't support Pixel for that long. But Samsung has been generally good with maintaining that four-year support for its models.
The oldest Samsung models to get monthly updates now are the Galaxy S10 phones. The company has already transitioned the Galaxy S9 and S9+ to quarterly security updates, which means these will get one more year of updates before these handsets lose support.