Using Classic Outlook on Windows for personal email, calendar, and contact management
New Outlook for Windows?
I'm starting this as a new Answer so we can keep the comments separate from the other conversations going on.
Have you ever tried the New Outlook for Windows App?
https://apps.microsoft.com/detail/9nrx63209r7b
I am not a big fan of New Outlook (vs Classic Outlook, what you are using now). But New Outlook has built in support for iCloud Accounts. It will sync your iCloud and Google mail, contacts, and calendar with no add-ins or other special handling.
I am only asking questions. I am not suggesting that you take any action at this point.
Before we go any further:
1 -- Have you ever tried New Outlook for Windows? If so, was there any reason why you could not make it your default email client?
2 -- Do you have any other accounts besides GMail/Google and iCloud/Apple?