XGS firewall log

The Packet Capture Log is not available as a Logfile. 
Could you give us some more insight, why you need this? 

Bare in mind, Central Firewall Reporting supports a more detailled view on this one.

The Logviewer is more a tool for "live debugging" and not a review of connection of the past 30 days. 

I use DNAT and the firewall's rule has enabled logging, but sometimes I find that the firewall does not have relevant access logs, so now I need to view the logs to analyze

I use DNAT and the firewall's rule has enabled logging, but sometimes I find that the firewall does not have relevant access logs, so now I need to view the logs to analyze

Try to take a look into Central Firewall Reporting.

Because it sounds to me, you are more interesting in Reporting than logging. Especially as logging only gives you entries, while this sounds like you want to have an overview to analyze.