If you run the desktop flow from a cloud flow, you can set a priority when launching it. If you use the Work Queue functionality, your items can also have priorities that you can modify. But other than that (and especially after a flow has already been queued) there is no way to change the priority in which it is picked up. It is essentially processed in the order in which it was invoked (triggered).
You need to build a workload management system to do that essentially, and handle priorities at the time when you invoke the flow. Using Work Queues is one of the possible ways to do that. Alternatively, it is also possible to build a custom solution, but it is arguably quite complex to do.
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