My friend can't join my Minecraft server that I set up on Mint

[Angvs]

Mint Version: 19.3.

I have the last version of Minecraft Java Edition for Linux and I've downloaded Minecraft Server from https://www.minecraft.net/en-us/download/server. I can create the server without issues via the terminal and log in into it with the IP address provided by command "ifconfig -a". But for some reason my friend cannot get in by the same address and instead gets the following error:

io.netty.channel.AbstractChannel$AnnotatedConnectException: Connection timed out: no further information:

I searched for this error over the internet and followed instructions on countless tutorials, but none seems to work. I remember succeeding in creating a joinable server numerous times in the past, but it is not working now for some reason. What should I do?