Hi @Mridk
Thank you for posting.
According to your description, you would like to attach files to task while new email arriving to a shared mailbox.
As you known, there is no area to attach files using ‘create a task’ or ‘update task details’. Thus, here is the workaround for your reference.
We should first save all fines to sharepoint library, and then insert sharepoint link into task. Once user click on this link, the sharepoint library will open and show attached files.
Flow overview:

Flow in detail:
“Scope If Email Has Attachments Save to SharePoint”

“Scope If Email Has Attachments Create Sharing Link”

For further information, you can check below article:
https://powerusers.microsoft.com/t5/Power-Automate-Community-Blog/Create-Planner-Task-and-Include-Attachments-From-Outlook-Email/ba-p/245121
Hope the content above may help you.
Best regards,
Anna