Are you running Parallels or Fusion or some other virtualization software to run Windows (or Linux)? Parallels, for example, can be set to over-ride the default browser (and mail) settings - redirecting such things to a virtual machine's browser ... and the shortcut business wouldn't work in that case.
Can't think of anything else - it should just work. Hopefully someone else has an idea.
Cheers,
Karl
PS I just tested with AC 12 and it works fine for me in Lion. Maybe there is something amiss with START edition...
AC 28 USA and earlier • macOS Sequoia 15.2, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB
One of the forum moderators