I dont know the answer, but I think people will pursue sections of the labour market which cannot (yet?) be automated. Why play video games that you're frankly sick of after a few months, if you could help someone out for both a social and comparatively large financial reward?

It would also depend on the specifics of how UBI would be implemented. Where I live I could stop working and live off welfare, providing a minimal standard of living. Yet almost nobody chooses this way of life as people strive for higher living standards, and for many work plays a part in giving meaning to life.

If more and more jobs get automated this might become a problem though, assuming no new non-automatable jobs are created.