backups larger than 500 gb create temporary files of equal size on the system disk
Welcome to the forum @hecgon
On Options screen 5, check Remote volume size to make sure you didn’t raise it to destination size. Default is 50 MB, although sometimes people have reasons to adjust sizes, as described in manual.
The backups will be split up into multiple files called volumes. Here you can set the maximum size of the individual volume files. See this page for more information.
What size is “equal size”? Equal is fine. Huge is not. Is everything OK below 500 GB (that’d be odd)?
There are advanced options such as asynchronous-upload-limit that set a limit on volumes in queue.
I’m assuming temporary files use dup-* names. Sizes vary, but many are about remote volume size.