As you know that an offline OST file fails to get opened in Outlook. Henceforth, the user can try either a manual process or third-party tool to open an OST file in Outlook with a whole mailbox to the advanced outlook 2019 version.
There are several third-party tools available online which can effortlessly open OST files in all editions of MS Outlook including Outlook 2019 to Outlook 1997.
Users can download the SysInspire OST Recovery software that restores other desired OST files and opens all mailboxes of the OST file in Outlook as PST file format with all email components.
Just you will have to select the OST File, scan and preview Offline OST file with email and items properties. Then, at last, open the OST file in Outlook as a PST file.
More info:- Open ost file in outlook 2019