You can migrate PST files to Office 365 without installing Outlook. One manual option is Microsoft's PST Import service, which helps you to upload PST files and map them to the required Microsoft 365 mailboxes through the Microsoft Purview portal. This process requires the appropriate permissions and a correctly prepared CSV mapping file. And for this, you need to have technical knowledge and it is time-consuming approach.

If you need to migrate multiple PST files or want to simplify the process, you can also use a dedicated tool like MailsDaddy PST to Office 365 Migration Tool. It helps transfer PST mailbox data to Microsoft 365 while maintaining emails, contacts, calendars, and other mailbox data. The tool support ANSI & Unicode PST files and migrate them into primary, sharedm in-place archive, and group mailboxes.