So, I've been searching for a while, to see if anybody has found a solution. I can confirm, this has to be something that was disabled by Samsung, in Touchwiz or whatever the heck they rebranded the UI to. I use Nova Launcher, but switched back to the Samsung UI, just to toggle off the Portrait mode, but that doesn't make any difference for the Wallpaper rotating. This has to be one of the biggest "fail" updates that I've seen Samsung do. What makes even less sense to me is that, the Tab S4 that I just purchased, has no problem rotating the wallpaper. Did they think that people just wouldn't need it for phones, so they just disable it?
If anybody has found a solution (either via app or side-loaded apk), please update on this post.
I noticed this on my Note8, now on my Note9, as well as my relatives that have S8's and S8+'s. I seriously don't know why they disabled wallpaper rotation, if they started offering homescreen rotation. It literally makes no sense, especially since their newest tablet offering does it without issue.