Both the Galaxy S8 and the Galaxy S8+ were released in April 2017. Exactly three years have passed since that time, which means that these devices will no longer receive the monthly updates that are provided for Samsung flagships. This is a logical order that complies with company policy.
According to this practice, Samsung flagship devices receive monthly security updates for three years, and after this, they are transferred to the quarterly update schedule. Such a schedule implies combining all of the security updates into one firmware update, which will be released once a quarter. The April 2020 security patch became the last monthly security update for the Galaxy S8/S8+.
In addition, Samsung devices should receive no more than two major updates of the Android OS. Since the Galaxy S8 and the Galaxy S8+ already received their second update last year, updating the devices to Android 10 is out of the question. In any case, for quite some time, these devices have not received any new features, so it is unlikely that the next update will carry anything more than a security patch.
As for the Galaxy S8 Active, it is still on the monthly update schedule. Since the device was released in August 2017, there is very little time left before it will face the same future.