You can import PST files into Office 365 using Microsoft PST Import service through the Microsoft Purview portal. The process involves creating an import job, uploading your PST files, and preparing a CSV mapping file to assign the data to the correct mailbox. However, the process take a lot of time and it require technical knowledge for doing multiple steps.
You can use alternative approach like MailsDaddy PST to Office 365 Migration Tool to transfer mailbox data to Microsoft 365. With this tool,
import PST files to Office 365 mailboxes while keeping the PST file mailbox data. The tool support all version Microsoft Outlook PST files and Windows OS.