Surely you cannot copyright "functionality" even in the US, is this not a bogus DMCA? Is there anything that average folk can do against these notices when they're sent to companies like GitHub?
They can file a counter-notice, commit to accepting service of process if the other party wants to sue, and wait 10-14 days. There's a guide at https://docs.github.com/en/site-policy/content-removal-polic... and there are plenty of example counter-notices in the https://github.com/github/dmca repo.