I was having problems on the syntax to get the axis labels with subindices and superindices, as it didn’t work as in ggplot2. The trick was to use a single expression() and specifying labeller = label_parsed)

Example:

resin_bv |> 
  ggpairs(columns = c("canal_size_bv", "canal_area_bv", "canal_density_bv"),
          columnLabels = c("Canal~size~(mm^2)", "Canal~area~('%')", "Canal~density~(n~cm^{-2})"),
          upper = "blank",
          labeller  = label_parsed) +
  theme_bw(base_size = 14)