I have never tried i2p before and am new to using Qubes but have somewhat intermediate linux (debian experience) user.
Anyway, I see PrestiumOS looks like a great option for an easy i2p VM…
but would like a way to learn how to setup and i2p Qube that only goes through i2p and doesn’t leak also.
I think you could make a new network providing qube where you install i2p or i2pd and allow its socket to be reached over network. Add a rule in the qubes firewall script to block all traffic except for using i2p socket.
Then attach a qube and configure the gateway IP to use i2p as a proxy in the program you where you want to use i2p.
I don’t think it’s possible to use i2p as a “vpn”, and it wouldn’t make sense because i2p is a closed network and not meant to be used to reach the outside world. (or at least, it shouldn’t be used for that to protect privacy)