Well, at first glance you have a data set (tibble) called variables and you are running a correlation on a data set called dat. I do not see any variable in the screenshot called "Perfs" but if it exists then
cor(variables$Perfs, variables$Clusters)
should work.
Screenshots tend to be close to useless. See
A handy way to supply some sample data is the dput() function. In the case of a large dataset something like dput(head(mydata, 100)) should supply the data we need. Just do dput(mydata) where mydata is your data. Copy the output and paste it here.