Hi Ignazio Castiglione,
Thank you for reaching out! I understand the importance of your query and I apologize for any inconvenience caused.
I checked from my end currently it isn't yet feasible to recover the contacts removed from the suggestion list because it is a dynamic, locally stored list of email addresses you’ve recently interacted with. It’s separate from your Contacts and is designed to "learn" from your emailing habits.
To re-add a removed address to the suggestions you need to Send an email, receive an email, reply to or forward an email, this re-triggers Outlook to add the address back to the Auto-Complete List.
Microsoft values such feedbacks as this one, could you keep submitting your valuable feedback directly to Microsoft product development team by either going to Help from your dedicated App > submit Feedback or by posting on Ideas · Community (microsoft.com) for feature requests. I will report to the appropriate team for a fix in future updates through internal channels.
Please note that nobody here are the product developers/decision makers and has no control over the product. Everyone, including us as community moderator, can only assist you on the query for providing available solutions and feature's availability status within our scope and capability.
To check more details about how to submit feedback, kindly refer this article Learn about how to provide feedback to Microsoft - Microsoft 365 admin | Microsoft Lear
Sincerely
Albert |Community Moderator