Hi, i've got the same problem and i cannot for the life of me understand why this is the case. When I purchased my tv, I paid more for a premium brand under the impression that it would last - the tv itself is perfectly fine but this type of forced obsolescence is infuriating and surely at odds with the current drive to be more sustainable.
But i shouldnt be surprised - I have a tv with software that has never had any updates in the 3+ years that I've owned it, and now i can't use it to access one of the biggest streaming platforms there is. I should expect that in a way - but not from a premium brand like Samsung.
I mean, TV's aren't items that people upgrade for the sake of it - they're not phones - and it's not as if an upgrade would be an insurmountable thing - i mean, i could probably go out, spend 100 quid on a cheap supermarket tv with considerably worse specs and be able to watch disney plus on it - but not on my Samsung which isnt even that old!
My TV - along with from the looks of it, countless similarly-aged Samsungs which work perfectly well apart from a lack of effort on your part - should be able to access Disney +. I know this won't go anywhere and the moderator will probably reply chirpily to this and tell me to buy an smart stick for a smart tv, but in the slightest hope someone important does see this, please understand that not every customer wants to go out and keep buying tv's when they've got fully working ones already, and update your software.
I really do understand your frustration, and I know that this is not what you would like to hear but the TV is not meeting the app system requirement. In this case, I would encourage you to reach the app provider to see if they will release any app compatible with your TV at any point. Alternatively, as @SaudA has mentioned you can access this using an Amazon Firestick, Apple TV Bos, PS4 connected to the TV, or by mirroring another device screen to it.