I have a fresh install of ArcGIS GIS Sever installed on Centos 1810 but I cannot connect.
The server has no firewall enabled, the curious thing is that I see processes on 6099 but not 6080 or 6443?
ArcGIS Server 10.4.1 supports a maximum Red Hat (or CentOS in your case) version of 7.2. See the following system requirements page: ArcGIS 10.4.x for Server system requirements—ArcGIS for Server system requirements | ArcGIS Enterpri...
This may not be the issue, but I believe the "maximum OS version" is specified there because of issues with 10.4.1 at higher minor releases of Red Hat.
Out of curiosity, what happens when you try to access an ArcGIS Server resource (let's say the Admin page) on the server machine itself? Does curl http:localhost:6080/arcgis/admin/login return anything?