You (probably) have a broken or non-existing registry. Try to remove and add again:
# Remove
rm(joinpath(DEPOT_PATH[1], "registries", "General"); force=true, recursive=true)
# Add
import Pkg
Pkg.Registry.add("General")
You (probably) have a broken or non-existing registry. Try to remove and add again:
# Remove
rm(joinpath(DEPOT_PATH[1], "registries", "General"); force=true, recursive=true)
# Add
import Pkg
Pkg.Registry.add("General")