Can I use Pearson correlation for discrete variables? Can I use Pearson correlation for discrete variables, if the level of measurement fits (either ratio or interval).
Thanks!

Sure!
set.seed(2022)
N <- 100
x1 <- rpois(N, 5) # Poisson(5)
x2 <- rpois(N, 7) # Poisson(7)
cor(x1, x2)

At no point does the Pearson correlation make distribution assumptions beyond the covariance and variances existing.
