Can't reach server from the outside on Linux only

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I have my Calibre content server successfully set up on Windows. It listens on port 27436 which I direct to from a reverse proxy on another server. SSL cert and stuff all working. So if my Windows is on I can connect to https://books.example.com and browse my library.

I just installed Linux on my personal PC for the first time as dual boot. I am running EndeavourOS which is Arch-based. I wanted to set it up so that it can read from my library and operate the server in the same way, so that regardless of whether I'm logged in to Windows or Linux the server runs.

I managed to set up the server on eOS and can access it via the external IP on my computer. However I can't seem to access it from the outside like I can on Windows via the same IP. I enabled traffic on the port in firewalld (also tried iptables and ufw) but I still can't access it. If I boot into Windows everything works properly so it's only a Linux issue. Does anyone have any ideas that I can try?

edit: forgot to mention that since it still works on Windows the port forwarding in the router is working correctly. I have verified that the internal IP of my PC stays consistent whether I'm on Windows or Linux so that port forwarding is working regardless of which OS I'm booted into.