Any firewall software you use that could be doing Deep Packet Inspection and thus be blocking some packets?

But you externally had the same port, didn't you?

Correct.

The port forwarding looks fine. Are other applications reachable from internet? Some ISPs only provide native ipv6 and carrier-grade NAT for ipv4, which doesn't allow port forwarding at all.

%appdata%\DDNet\Videos

It shouldn't, but if you can try unplugging all devices it might help

Use lan cable instead of wifi, disable powersaving for network adapter, turn off other computers, stop other programs.
https://wiki.ddnet.org/wiki/Troubleshoo ... n_problems

Never heard about this issue, on official servers? Try another server location.

Try to update your AMD GPU driver and switching between Vulkan and OpenGL in graphics settings.

Hopefully will be done by end of the month.