G'day EigenFunctions,

"When I run CPAN, both end with a Checksum error as shown above."

[Note: CPAN is a core module; you won't be running that. I'm going to assume you meant the cpan utility.]

You've encountered the security vulnerability CVE-2020-16156. There are a number of references near the end of that page; the most pertinent for you is probably "Addressing CPAN vulnerabilities related to checksums".

This has cropped up a few times here. I first encountered it in 2021. The information in the subthread "Re^4: pod2html: link (L<...>) formatting code (timeloop)" may be useful to you when fixing the problem; it contains the same "The cksum does not contain the key 'cpan_path' for ..." message.