This is all our own opinion. I look after a fleet of 1250s which are used for Blood Biking in the UK. We have 2020s and a brand new 21. As I said I own a 2019 1250 which I ride all year around. There is no difference in the active suspension or how the bikes perform. Today I was out on a 20 1250, tonight I have been on duty on the 21, I can feel no difference in how it handles or how the active suspension performs. There are no reviews I have seen that state the 21 1250 has any performance gains over a 20 1250 or pulls differently. The only software difference is with the TFT, there is no mapping difference at all, all the bikes get the same engine mapping updates.
I agree that there isn't adaptive cruise, but our 21 doesn't have that either. Personally and I again state this is my personal view, I do not like adaptive cruise, I have it in my car and prefer the normal cruise, I certainly am not bothered about it on a bike. But if those things are important to you, then yes it is different. The lights are an improvement, LED vs Halogen.
I also prefer the dials over a TFT. TFTs are getting stolen in the UK as they just pull off and they are a £1200 replacement item, although thieves are targeting GS bikes at the moment, but that wouldn't stop me buying one with the TFT. Even the exhaust flap and headers are the same part number and still stick open.
But as I said, if the differences are what you want, then go for it. I wouldn't upgrade now, if I was considering it, I would hang on until there is an appreciable difference, there will be a new model coming and there is already strong indications the GS will be getting a 1300 engine very soon, which means the RT will follow.