I did this back when I was using all Android mobile devices, but all Mac desktops/laptops (4+ years ago).
Worked nicely, but required some additional purchases/subscriptions. Easiest/most secure back when I did it was with mailbox.org account, forgot the name of the Android app. Was seamless (bi-directional) as all iCloud services. Make an appt addition on Android, showed up in Calendar, and vice versa. Less than a minute sync time. However....the colors weren't exactly the same, but it didn't bother me.