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As always, test these updates in a lab first! I recommend checking out this 7-part guide on configuring Exchange in your lab. It doesn’t take much to get one going.
The updates are as follows:

Exchange 2019 Cumulative Update 5 (VLSC)| KB4537677

Exchange 2016 Cumulative Update 16 | KB4537678 | UM Language Pack
So, what’s new in these Cumulative Updates?
In this series of cumulative updates, Microsoft has resolved a number of security and non-security issues. You can read more about those in KBs 4537677 and 4537678.
This series of cumulative updates shipped with a new version of the calculator for Exchange 2019. This new calculator corrects an issue where developing a design around mailbox size or IOPs was not producing the correct number of mailboxes per database.
Cumulative Update 5 also corrects an issue in the Manage-MetaCacheDatabase.ps1 script that ships with Exchange 2019. The script has been corrected to only return solid-state disks that are initialized. It does this by filtering out all disks with no disk number. This issue was first identified in this article.
These Cumulative Updates also fix an issue with how cookies are handled in Google Chome 80 and later. The SameSite cookie issue was first identified in this post.
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