These are valid concerns and the devil is in the details. As I’ve noted elsewhere, some right-wing libertarians and Tulsi Gabbard like UBI as a means of abolishing the social safety net.
Jobs for all isn’t a terrible idea but what would such jobs entail? What kind of work would people be doing? Stalinist economies used to provide a kind of ‘jobs for all’ and they basically collapsed because economically it wasn’t feasible to keep unprofitable enterprises open at the expense of profitable ones in the long run.
UBI/BIG could be viewed as a subsidy to employers, but if everyone has a UBI that guarantees what today we call a living wage, why is this a problem? Is the purpose of public policy to make employers pay or to make sure everyone enjoys a decent standard of living? If we have a robust UBI program coupled with a strong welfare state (like the Nordic countries, say), surely that will relieve employers of providing ‘extras’ like healthcare or even a portion of wages — why is that bad?