Hi! At the moment I don't have any information if the S9 will get the new Android 11 update. I have posted a complete list that will be updated each month with coming and completed models. Keep an eye there for any new info!
Yeah, Samsung guarantees 2 major OS updates, and security updates for 3 years. So when it comes to your S9+ it seems like there will not be any more major updates. If you are really keen on getting the latest with Android 11 and not afraid of loading some customs roms there are possibilities as with "Noble ROM" (google it at your own risk). However this is not official fw and not supported by Samsung (maybe ElinH will slap my fingers now) - I just wanted to say that your S9+ still is a pretty darn good phone, and there _are_ possibilities to upgrade, even if not official. However, I would stay with Android 10 and enjoy that stable version of Android and One Ui rather than getting into Custom Roms again (I've been there, and it can be a smooth ride or a very bumpy road, and the only way to know is to try and maybe cry afterwards...)
This is not bad. Samsung has had 2 major updates for years and s9 in s series are last modell getting 2 major updates before samsung went out official to give from s10 and note 10 and upp 3 major updates and 5-7 years security update. Also there is a reason why s9+ won't get it, since alot of manufactures test older devices with newer android and when they see it's slow and lagy and not running smooth then that is reason they decide to not updating it to newer version.