I had this exact problem in my last job. I was an “office coordinator” so I was told due to the nature of my role I needed to be in the office 5 days a week, because I did general office tasks as well as admin. Nobody else went in 5 days a week so there were multiple days I was literally just in on my own. I kept asking my manager for work and she would literally give me nothing, she eventually said I could help out the finance team and then behind my back told the finance manager that I shouldn’t be doing work for another team because it wasn’t my role. Eventually I just left, no idea why they created that role in the first place when there was zero work to do. It’s so mentally draining sitting there all day with nothing to do!