Unable to assign logstash aliases to index

[logger (Malte Leek)]

This should not be a problem. But maybe you try the syslogs input.

Syslog input plugin | Logstash Reference [8.11] | Elastic

you only need to use

input {
syslog {
port => 5514
type => syslog
}
}

Try this and show me the error, if there are any.