When people say Office 365 migration mostly they are talking about exchange migration. It does not include other components of Microsoft 365 like Teams, SharePoint, OneDrive etc. For mailbox or exchange migration there are 4 approaches:
Depends on what service you are targeting, exchange, SharePoint? If SharePoint, depends on the version you are migrating from. Manual Migration, Tool Based, SharePoint Migration Tool by MS, Migration API.
IMAP, Cut-Over, Staged, Hybrid and Express Migrations