http://cs.i2p/faq
The only VPN protocols we use are OpenVPN and WireGuard, so we support whatever they do. At the moment, for OpenVPN, that includes: Linux, Windows XP/Vista/7 and higher, OpenBSD, FreeBSD, NetBSD, Mac OS X, and Solaris. Officially, we no longer support Windows XP, but it is still possible to connect with it.