To merge multiple PST files in Outlook 2019, follow these steps:
Open Outlook 2019 and click on the "File" tab in the top left corner.
Click on "Open & Export" and then select "Import/Export".
In the "Import and Export Wizard" window, select "Import from another program or file" and click "Next".
Select "Outlook Data File (.pst)" and click "Next".
Click on the "Browse" button and select the first PST file that you want to merge.
Check the box "Do not import duplicates" and click "Next".
Select the folder that you want to import and check the box "Include subfolders".
Choose "Import items into the same folder in:" and select the destination folder in your Outlook account.
Repeat steps 5-8 for each additional PST file that you want to merge.
Once you have selected all of the PST files that you want to merge, click "Finish".
Outlook will begin importing the data from each PST file into the destination folder that you selected. This process may take several minutes, depending on the size of the PST files.
Once the import process is complete, you should see all of the data from the merged PST files in the destination folder that you selected.
Greetings,
Peter