Hi @user55521 ,
I think it depends on your license, there is no limitation from AEM Cloud AFAIK (It will just forward it). I suppose the free tier of Splunk has some limitations around 500MB.
The network bandwidth associated with logs sent to Splunk is considered part of the customer’s Network I/O usage.
You could check these links for more details:-
https://experienceleague.adobe.com/docs/experience-manager-cloud-service/content/implementing/developing/logging.html?lang=en#splunk-logs
https://www.opsinventor.com/using-splunk-for-log-search-monitoring-on-aem-as-a-cloud-service/
If you need to know what log size you have currently generated on your instances which will be forwarded, the best way would be to raise a support ticket.
Hope this helps!
Regards,
Nitesh