It's not "compatible" with the old network, but you can get it to work
with the APNs provided on Reddit. I have heard that there may be
problems and it might not work on the new Visible network though (which
is required soon).
I've been avoiding "upgrading" as I have zero issues with my Galaxy S10+
right now. I'm hearing that it just doesn't work on the new network,
despite any attempts to change the APNs.