Cannot set/select custom font family

[mdevDE]

3.1.71

When trying to select the custom font family "OS System Font" it is not set after selection

font: {
list: {
"font-family: -apple-system,BlinkMacSystemFont,Segoe WPC,Segoe UI,HelveticaNeue-Light,Ubuntu,Droid Sans,sans-serif;": "OS System Font",
"Helvetica,sans-serif": "Helvetica",
"Arial,Helvetica,sans-serif": "Arial",
"Georgia,serif": "Georgia",
"Impact,Charcoal,sans-serif": "Impact",
"Tahoma,Geneva,sans-serif": "Tahoma",
"'Times New Roman',Times,serif": "Times New Roman",
"Verdana,Geneva,sans-serif": "Verdana"
}
}