Alexa on my iMac desktop

All Apple has available is for iOS and iPad OS:

I found numerous third-party apps that "claim" to allow desktop access to Alexa but I view using these about as wise as letting the toddler play with a rattlesnake. A huge amount of information about you goes through Alexa and you DON'T want that info going through an app that is connected to an unknown server.

If Amazon does not offer it, do without.

There is no Alexa app for macOS, but you can access and use Alexa from your Safari browser.

check out > https://www.youtube.com/watch?v=LTz587LHdpU

IOS and Mac OS are different OS's and unless the developers develop apps that run on both platforms you cannot run an IOS app on your Mac.