Hello sns,
#1 I would recommend (if possible) to start migrating data to SharePoint Online (M365). For this, I would recommend using SPMT (SharePoint Migration Tool):
Overview of the SharePoint Migration Tool (SPMT)
https://learn.microsoft.com/en-us/sharepointmigration/introducing-the-sharepoint-migration-tool
#2 If you are really wanting to go down the path of migration to SharePoint 2016, I would recommend reaching out to a company who has experience migrating data.
#3 If you want to do this yourself, take a look at the following PowerShell script:
Migrate Network File Share to SharePoint using PowerShell
https://www.sharepointdiary.com/2020/03/migrate-network-file-share-to-sharepoint-using-powershell.html
If this is helpful please accept answer.