The data is transferred to your Browser, and now your Browser starts working to set up the report nicely in your browser, first, you will see the total figures.
Hereafter it will start sorting your data, eg in my example, to split the calls for each 60 Minutes pr. Day. Please note, this part does take Resources from your Local PC, and the time to generate, does depend on the number of calls, and the selections for your sorting of the calls in the report.
It seems to be just about the same resources used if you are using Chrome or Edge, in our case approx 90% CPU to build the report, and over quite a long time, for this report with a total of 264.935 calls.
Find more Reports info in the posts below