A few months ago there was news that Samsung could upgrade the Galaxy S6 to Android 8.0 Oreo, but it looks like it is not.
What is known
On the official website of Samsung Mobile Security there is a section with monthly and quarterly updates. In the first section there is a list of smartphones that receive them every month. Basically, these devices are S and Note-series, as well as several A-series smartphones. In the second - budget, medium-budget smartphones, as well as tablets. If these devices disappear from the list, they will most likely no longer receive updates.
The other day, they lost four smartphones: Galaxy S6, S6 Edge, S6 Edge + and S6 Active. But then Samsung updated the lists again and returned the S6 Edge + and S6 Active. Perhaps because they came out later.
Recall that the Galaxy S6 came out in 2015. The smartphone was equipped with a 5.1-inch screen with a resolution of 2560 × 1440 pixels. The performance of the device was answered by the Exynos 7420 processor. In S6, a 16 megapixel camera with f / 1.9 aperture was installed. Initially, the device worked on Android 5.0.2 Lollipop, and then updated to Android 7.0 Nougat. The S6 Edge version had the same characteristics, but the smartphone had rounded edges of the screen.