If you're looking for a fast and reliable solution to convert OST files to PST format, try the GoldyTools Exchange OST to PST Converter. This efficient tool is designed for both technical and non-technical users—no professional experience is required to perform the conversion.

With just a few simple steps, you can easily convert your OST data to PST without any risk of data loss. The software also offers a free trial version, allowing you to test its features and performance before purchasing. The trial version enables you to export the first 25 items from each folder completely free of charge.

GoldyTools OST to PST Converter is fully compatible with all Windows versions and supports all editions of Microsoft Outlook, including Outlook 2021.
https://www.goldytools.com/blog/how-manually-convert-ost-to-pst-files-in-outlook/