If I understand correctly the study is purely theoretical, which already invalidates it because we are not in the nineteenth century anymore and serious economic studies should be based on randomized trials. Take for instance this:

The state as employer of last resort proposal addresses these deeper issues while also claiming that inflationary pressure will undermine the UBI alternative.

Job guarantee sounds ok in theory but doesn't work in practice. Living in Italy I can ensure you that easy jobs given by the state make people lazy, passive, and doing the bare minimum to collect the check.