Symptoms
In the Korean version of Outlook on the web, if you open an email message that contains multiple recipients in a web browser that's configured to be viewed at less than 100 percent, some recipient names are displayed incorrectly as "+number 개 더" instead of "외 number 명" as expected.
Resolution
To fix this issue, install one of the following updates:
Cumulative Update 11 for Exchange Server 2019 or a later cumulative update for Exchange Server 2019
Cumulative Update 22 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016
References
Learn about the terminology that Microsoft uses to describe software updates.