Hello @S3VC ,
The email builder within the event builder is an older system, so invites explicitly built within an event won't have mobile friendliness coded into them. You are able to access its HTML, and contacts sent an invite will be shown in the event's invited contacts - making it so you can send follow-up emails that explicitly target invited contacts that haven't registered or declined yet.
For more info on creating these types of emails
With that said, if you're more concerned about the mobile friendliness of the invites, you can utilize the regular email builder, and simply add the share URL as a text, image, or button link. Sending an "invite" in this way won't generate a specific "invited" or "declined" list within the event, but it will still keep track of actual registrants.
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