Monitoring log files using some metrics exporter + Prometheus + Grafana

Take a look at Telegraf. It does support tailing logs using input plugins logparser and tail. To export metrics as prometheus endpoint use prometheus_client output plugin. You also may apply on the fly aggregations. I've found it simpler to configure for multiple log files than grok_exporter or mtail

Those are the 3 answers currently for getting log data into Prometheus.

You could also look into getting whatever is producing the logs to expose Prometheus metrics directly.