This is absolute nonsense. If you're non-disabled (which is not even a thing), how would anyone know and use that to shut down redreader?
Also, redreader is NOT specifically for disabled people (again, not a thing). It just happens to have features which are useful for people with certain impairments. That is enough to be considered "non-commercial, accessibility focused" enough for access to the API.
In short, use it if you want. Also read up on the social model of disability and the kerb cut effect.
The are approximately infinite ways to solve this "problem", starting with how you even define it. If it's unsustainable at current levels, what does sustainable mean? Is the time period this year, fifty years, a thousand? What's the gap? Does it include administration costs, or just the payments?
Once you define what the question is, you can start to answer it. We could increase immigration (very good point btw). We could raise taxes (if so, which tax? Corporation? National insurance? If so - employer or employee contributions?). We could raise interest rates. We could remove the triple lock. We could just murder everyone over 75. We could do a mix of everything - raise taxes a bit and only murder the over 80s.
How you answer the question depends a bit on facts and a lot on ideology. The fact that this article takes one potential solution and declares it THE ONLY solution tells you a lot about their ideology.
The podcast "the news agents" had a good bit where they played a clip of Andrea Leadsom saying categorically this would not happen, followed by Leadsom saying "we knew this would happen all along".