SharePoint 2016: Databases running in compatibility range, upgrade recommended

You may notice the above comment when you create a brand new farm in Central Admin under Central Administration->Upgrade and Migration ->  Review database status

On a new farm without any site collection you should have the Sharepoint_config  configoration database and the Sharepoint_AdminContent_***    content database.

the Sharepoint_AdminContent_***    content database is the one with the status Databases running in compatibility range, upgrade recommended.

you can also view more details on the event viewer :

You have performed an initial core install of SharePoint 2016 onto a single server. You have not yet created user content web applications or instantiated any service applications. Later, you check Health Reports and notice the following warning:

Title Databases running in compatibility range, upgrade recommended
Severity 2 – Warning
Category Configuration
Explanation The following databases have versions that are older than the current SharePoint software, but are within the backwards compatible range:
[central admin content database].
Remedy To achieve optimal results from these databases, use Upgrade-SPContentDatabase to upgrade Content databases, or psconfig.exe to upgrade other databases. For more information about this rule, see
Failing Servers
Failing Services SPTimerService (SPTimerV4)
Rule Settings View


To fix this you can run the following code :

Add-PSSnapin Microsoft.Sharepoint.Powershell
stsadm.exe -o localupgradestatus # get detailed information on database status
# get all databases since the admin content db doesn't considered as a regular 
# content DB and won't show in Get-SPDatabase without the -Auto command
Get-SPDatabase | ft -Auto 
Psconfig.exe -cmd upgrade -inplace b2b -wait -force # upgrade databases

Ref:  Microsoft TechNet