Can I migrate a tenant site, site collections from ABC.com to def.com (both are of O365) without using any third-party softwares. If yes, the procedure please. Also,Can I do it by backing up and restoring method through PowerShell. ?
In reality, no. You will need a content migration tool to effectively do this without loss of data fidelity or metadata. For example, if you were to copy documents using the Explorer view, you would lose the modified time, who the document was created by, and so forth.