These are solely based on the copilot license purchase and are configurable and can be adjusted for custom agents on case-by-case basis.
Ref: https://learn.microsoft.com/en-us/microsoft-copilot-studio/requirements-quotas
If Microsoft 365 Copilot license is present: files up to 200 MB.
If Microsoft 365 Copilot license is not present: files up to 7 MB (* Larger files can be supported via implementing custom code solutions)
Files with sensitivity label as “Public,” “General Business” are supported.
Files with sensitivity label as “Confidential,” “Confidential – Internal or External Recipients”, “Restricted – Named Recipients Only” are not supported.
Files with sensitivity label as “Personal” are supported conditionally only i.e. based on logged in user and author/manager of the document.
Encrypted files are not supported.
SharePoint’s Access control list is in check w.r.t logged in user interacting with the copilot.
If user does not have access to the SharePoint site/pages/files acting as a knowledge, then for an user’s query copilot may respond with “No answers found.”
* For any kind of on-prem tools/data, further feasibility may be required.