If you have web parts that are referred to other lists/libraries/documents/items in this or other sites, or other type of web parts that do not rely on themselves, the components will not be carried over to SharePoint Online, regardless of the migration tool you are using.
Consider doing a migration to the whole site in order to bring the web parts along with the pages.
You can use SharePoint Migration Tool (SPMT) and select "Migrate all lists, libraries, pages and web parts" under "Content you want to migrate".
It will retain the version histories of the pages as well.
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