You can have M365 without email migration. If you don't want to move email to Microsoft 365, you can simply purchase licenses for SharePoint Online (standalone) or Microsoft Teams (which includes SharePoint features) for those who need it. You don’t have to utilize the Exchange Online portion of the license. Your on-premises Exchange can continue to operate as is.
OneDrive for Business is also an option. OneDrive for Business can be licensed separately from the full Microsoft 365 suite. It offers co-authoring functionalities when used with Office desktop applications. By doing this, users can collaborate on documents in real-time while keeping email on your on-premises Exchange.
Office for the web I think is free, that could be an option (not sure of it, haven't looked into it and it's been awhile).