Could you elaborate your needs?
Is it okay if the flows run one at a time? If so then you need just one bot and you can run it on virtual machine (attended or unattended).
When you start the flows from the cloud your flows will run one at a time since Power Automate sees that the machine is occupied by other flow run.
So if you have Flow A that starts Power Automate Desktop (PAD) flow and Flow B starts while Flow A is still working on the virtual machine the Flow B will not try to start PAD flow until the Flow A is finished and logged out of the machine.
If you want to have multiple bots running at the same time you need to have Windows Server so you can have the bots log into their own sessions and run parallel to each other.
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