Under that scenario if seventy five percent of the population is receiving a basic UBI that enables them to just get by then it would only seem logical that those using technology that put that seventy five percent out of work could only utilize that technology at twenty five percent of it's capacity. Would they then also be limiting themselves to a self imposed UBI of their own that may pay better than a government UBI but still nowhere near where they could be if they hadn't made it so seventy five percent of the population can't buy their product.
100 percent receive a UBI which is what makes it universal. Universal doesn't mean everyone in the world though. For example, Finland (where I live) could implement it but Sweden might not. All Finns will get it, no Swedes.
The capacity comes from automaition and AI. The 75% aren't needed at all except as consumers.