Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Dear Agustin Derecho,
Greetings!
Thanks for reaching out to this community.
Based on your description, I understand your issue with email missing after creating new folder.
You may first try to sign into Outlook on the web. Then you can search/check all your folders there and see if the missing mails can be found there.
If the above method failed to you, since it seems you are using a M365 business account, it's suggested to contact the admin of your organization to create and run a content search in Microsoft Purview compliance portal to search for these mails (by entering a keyword query and adding conditions to the search query if necessary) in your Exchange mailbox. (If you are not sure who is your admin, can refer this How do I find my Microsoft 365 admin? - Microsoft Support).
For more instructions, please kindly refer to Get started with Content search | Microsoft Learn.
Thank you in advance for your understanding! At this time, your patience and cooperation will be greatly appreciated. I hope all the best!