It’s important to note “Modern Monetary Theory” (aka MMT) is almost unanimously rejected by mainstream academics[1]. Its largest proponents are political leaders rather than economists.
It's also important to note that main stream academics all thought the stimulus during the financial crisis would be inflationary, and they were wrong. Now, I'm not advocating for the government to print money galore since more dollars chasing fewer resources means inflation, but I think there's a decent case to be made that the current debt level is sustainable if we can gain efficiency to match the rate of currency growth.
Also, I should add--I do not think UBI is a wise path.