I2P support forum

I have IPv6 open to my router port and IPv4 firewalled. With an IPv4-only configuration, I had almost no participating tunnels (I think that I saw one once).

I see two network configuration settings that apply to my situation. First, under IPv4 Configuration, there is a checkbox labeled "Disable inbound". I assume I should check this.

Under IPv6 Configuration, I see an option labled "Use IPv6 only (disable IPv4) (Experimental)". If I select this option, am I helping anyone? Or should I just not "experiment"?

Best to leave everything the defaults. I2P knows you are IPv4 firewalled, and you can still use it for outbound, and with SSU2 relay you can still get peer-assisted inbound connections.

Correct. However even with gigabit direct IPv6 your router will only get a small fraction of traffic compared to those with direct IPv4. I2P(d) has a rating mechanism for peers that works this way.