Thanks for that piece of information. Since I dropped macOS usage, I haven't kept abreast of that type of news.
My understanding is that Perlbrew requires Perl to be present for its initial installation. Subsequent work with Perlbrew — upgrading, installing new Perls, etc. — can utilise a Perl already installed by Perlbrew. I've used Perlbrew for a very long time and have always had some sort of system Perl to kickstart the process, this includes: macOS as just described; Cygwin on my current and past setups; and, Linux on my $work machine.
I had a look at "Perl Download". From what it has there, it looks like ActiveState Perl might be the best way to install an initial Perl from which Perlbrew can be run. The Mac Pro that I previously had has been cannibalised to the extent of being completely non-operational; I have no way of running macOS at the present time.
For future reference by those starting with macOS v10.15, or a later version, it would be helpful it someone could comment on the best way to start the Perlbrew process.