The SharePoint Migration Tool (SPMT) is a tool that migrates your files from SharePoint on-premises document libraries or regular file shares and easily copies them to SharePoint in Microsoft 365. It is available to all Microsoft 365 users.
In Microsoft 365, tenants you can control whether users can run custom script on personal sites and self-service created sites.
During migration, some web parts require this setting set to allow. Otherwise, the web part will not be migrated.
At least 24 hours before you start migration, do the following:
Go to the Settings page of the new SharePoint admin center, and sign in with an account that has admin permissions for your organization.
At the bottom of the page, select classic settings page.
Under Custom Script, select:
Allow users to run custom script on personal sites
Allow users to run customer script on self-service created sites
Leave these settings in place for the duration of your migration.
To install the current release download, go to: SharePoint Migration Tool
Migrating data files from SharePoint Server document libraries
Start SPMT, and then enter your Microsoft 365 username and password.
Select Start your first migration.
Select SharePoint Server.
Enter the SharePoint Server site URL where your content is located, and then select Next.
Enter your username and password to the SharePoint Server site; username must use the format of email@example.com. Select Sign in.
Select the document library where your files are located. The dropdown contains all your possible choices.
Enter the URL of the SharePoint site where you want your files migrated.
Select the document library to where your files will be copied.
Select Add. This task is added to the list. If you want to select another set of data files to migrate, select Add a source. Learn about how to migrate SharePoint 2010 to SharePoint Online in detail.
I hope these steps will be helpful!