If you run through that guide I think the intended result is that "Alt-C" is going to be your copypaste. E.g. the keys work in the Mac order: CTRL / OPT (ALT) / COMMAND instead of the Windows order (CTRL / WINDOWS / ALT). So using Alt-C should trigger Copy, matching Mac-user muscle memory.

Perhaps PyCharm is set to Windows keymappings or such?

The mac doesn't use ctrl modifiers to use copy paste. If you remapped Alt/option and windows/command keys on a windows keyboard alt-c & alt-v (i.e. the keys to the right/left of the spacebar) would be recognized as cmd-c and cmd-v on the mac. PyCharm supports a windows and linux keybinding that lets you use ctrl-c and ctrl-v to copy paste but the mac generally uses the cmd key as opposed to the ctrl key. If you want to use ctrl-c and ctrl-v you can remap both of those pretty easily using karabiner elements to cmd-c and cmd-v.