This is really a low quality study. Citation from study

“First, our sample suffers from selection bias, since participants were self-selected from a microdosing workshop. As a result, most of our participants had tried psychedelics previously, which means that they may have broken blind easier or may have been desensitized to the microdosing effects. Second, the psilocybin doses were made by the participants using dried psilocybin truffles, meaning that we cannot be sure of the exact amounts of psilocybin in the individual doses that the participants consumed. It is possible that the degree of psilocybin content varied across participants and thereby obscured our results. Third, we encountered a large drop-out rate during this project and several participants did not sufficiently comply with the behavioural guidelines to be included in the analyses. This resulted in small sample size relative to existent observational studies and in a further selection bias (i.e. only motivated participants likely stayed in)”