There are lots of problems related to photoelectric effect, which, for example, use, or have as answer, a work function of less than 1 eV. But when I search on Google, I found out that most metals have work functions greater than 2 eV, let alone reach between 1-2 eV. So is the work function in the problem just made-up, or is there a material with work function less than 1 eV? I also found this but it was released 8 years ago, so I don't know if it's outdated.
I think most of the materials have work function above 2 eV (most common materials). The poster you shared, I don't think it is outdated. Of course, a lot of materials can be made and synthesized with different work function values. And as I see on the poster, there is no material with work function less than 1 eV. The plot has a minimum of ~ 1.8 eV.
P.S.: in (especially, theoretical) physics problems, of course, any work function can be used.
EDIT: Here, one with less than 1 eV (it is a bit old): https://aip.scitation.org/doi/abs/10.1063/1.1652810?journalCode=apl and pubmed.ncbi.nlm.nih.gov/28681728
1.5 eV also exists. But less than 1 eV work functions, sounds unfeasible. That means that a material should have very weak bound electrons, which can easily be rejected from the material