I am a Linux user. Bizarre assumption to make given my excitement over a Wayland specific Discord feature. But I don’t have any actual qualms with how Discord implements its own services. Matrix just doesn’t fit the bill for me. If you enjoy it, and it suits your needs then all the power to you. It just isn’t what works for me.
Because you’re serving the website on a non-standard port, you will always need to provide the port in the web browser.
That said, I don’t see anything wrong here. It looks like you’ve got the right ports set, TCP should be correct. You may not get a ping, because ICMP is likely not enabled at the modem. When you ping, you ping the first device that’s exposed to the internet, not an open server.
Just to be sure, when you’re on your phone, you’re using data? If you’re on wi-fi, the modem/router may not be configured to perform NAT reflection, so you won’t be able to access anything via your WAN IP.