I tried to host a room to play with my friend but somehow he can’t connect to that room. The same thing happen when I try to connect to his.
In order for us to provide better support, we need to see the log generated by Citra. This guide will walk you through how you can obtain the log file: How to Upload the Log File.
That means the port has not been port forwarded correctly in your router. If you are unable to do so, you can try use like Hamachi or ZeroTier and host unlisted instead, connect with Direct Connect to Room and put in the virtual IP which is generated by these software. Create a virtual network and invite him to it.