Hello !
I went a little deeper into the issue of USB ports and hubs. I would have liked to have given a more precise answer in the case you were describing.
Each USB controller has a roothub, to which several physical ports can be connected by the same bus; all ports connected to the same controller will then have to share the bandwidth of the same bus.
Motherboard designers adopt a more efficient design, and choose to connect the USB ports to different controllers, when they are available on the chipset, in order to provide dedicated bandwidth for each port, or for each group of two ports for example.
All this to confirm that the "hubs" you see on your machine are quite normal, these are the roothubs through which the ports are connected to the controllers, and they are found on all machines. They should not prevent the Plop's boot manager from working.