After Upgrading to 4.0.3 i get this errormessage in systemcheck.
after searching on the net i found
Matomo Issue #16804 - Matomo 4.0.0 warns about “ExampleTheme requires Piwik <4.0.0-b1”
an deleted the Example* folders.
but the errormessage is staying.
the suggestion is to wait until cache expires. after some tim the message disappers .