To launch a new portal from existing portal go to existing portals harness->scripts and styles->create a type js file with some name and paste code as below.

create a text file with code as below.

function SwitchNewPortal(e, f, c) {
    if (e !== f) {
        if (null == c || 0 >= c.length)
            c = e;
        var l = pega.u.d.fieldValuesList.get(c);
        "undefined" === typeof l && (l = c);
        c = pega.u.d.fieldValuesList.get("SwitchPortal") + " " + l + " " + pega.u.d.fieldValuesList.get("PortalText");
       
            c = SafeURL_createFromURL(pega.desktop.pzProcessPortalSwitch);
            c.put("portal", e);
            c.put("Name", f);
            c.put("developer", !1);
            c.put("switchPortal", !0);
            pega.ui.composer && pega.ui.composer.isComposerPreviewFrame() && c.put("isPreviewFrame", !0);
            if (e = pega.desktop.support.getDesktopWindow())
                e.logout = !0;
           // window.location.href = c.toURL()
          window.open(c.toURL(),"_blank");
        
    }
}
//static-content-hash-trigger-GCC

Now add a button in portal with a button on click run script ->SwitchPortal

Add 2 params below that function as below

param1 ->under value pass portal name hardcoded (example: User)

param2->pyPortal.pyOwner

declare pyPortal in pages and classes to Data-Portal class.