Very similar to a recent Community question, so be sure to search first.
You can't do this kind of pattern matching. I recommend maintaining a separate custom field for the public domain suffix. You can populate this field using a webhook or import/export, or if you use SFDC you can compute it there. The more fields you split it into, the easier it is to use Marketo's rather limited string matching rules.
Apologies, I should have searched through the community questions first. I am a new user so I don't know the guidelines/navigation.
Also thank you so much for your response, I will make sure to implement your suggestion.