For others having the same issue, found a solution:
In Julia REPL,
import Pkg;
Pkg.add("Conda")
import Conda
Conda.update()
Pkg.build("PyPlot")
No idea why was that necessary but the code now works. Though I’m still getting a warning, no idea if there’s any consequence.
[ 1 ] alexandre@Alexandres-MacBook-Pro Desktop ./test.jl
[ Info: Installing pyqt package to avoid buggy tkagg backend.
┌ Warning: No working GUI backend found for matplotlib
└ @ PyPlot ~/.julia/packages/PyPlot/XaELc/src/init.jl:165