I2P is designed to be relatively resilient against blocking.
Unlike Tor, there is no central directory of nodes, any floodfill
router might have an incomplete view of the network state, all nodes
participate in routing.
You will have to run some kind of Deep Packet Inspection to catch it,
which Qubes does not support.
https://geti2p.net/en/docs/how/threat-model - see section on
Identification of traffic.
This question is not related to Qubes development and should rather be
asked elsewhere.
https://geti2p.net/en/contact - good starting point.
Good luck,
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Radosław Szkodziński