dockers iptables rules limit upload speed to 500 mbit on I219-LM network adapter

root@Ubuntu-2004-focal-64-minimal ~ # lspci | egrep -i --color 'network|ethernet'
00:1f.6 Ethernet controller: Intel Corporation Ethernet Connection (2) I219-LM (rev 31)

root@Ubuntu-2004-focal-64-minimal ~ # speedtest

Speedtest by Ookla

 Server: Radio Town - Helsinki (id = 43442)
    ISP: Hetzner Online GmbH
Latency:     0.33 ms   (0.02 ms jitter)

Download: 938.09 Mbps (data used: 423.1 MB)
Upload: 487.48 Mbps (data used: 256.9 MB)
Packet Loss: 0.0%

root@Ubuntu-2004-focal-64-minimal ~ # iptables -S
-P INPUT ACCEPT
-P FORWARD DROP
-P OUTPUT ACCEPT
-N DOCKER
-N DOCKER-ISOLATION-STAGE-1
-N DOCKER-ISOLATION-STAGE-2
-N DOCKER-USER
-A FORWARD -j DOCKER-USER
-A FORWARD -j DOCKER-ISOLATION-STAGE-1
-A FORWARD -o docker0 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -o docker0 -j DOCKER
-A FORWARD -i docker0 ! -o docker0 -j ACCEPT
-A FORWARD -i docker0 -o docker0 -j ACCEPT
-A DOCKER-ISOLATION-STAGE-1 -i docker0 ! -o docker0 -j DOCKER-ISOLATION-STAGE-2
-A DOCKER-ISOLATION-STAGE-1 -j RETURN
-A DOCKER-ISOLATION-STAGE-2 -o docker0 -j DROP
-A DOCKER-ISOLATION-STAGE-2 -j RETURN
-A DOCKER-USER -j RETURN

I installed docker using the offical repository:
https://docs.docker.com/engine/install/ubuntu/

Clean minimal installation, just installed docker, no containers.

No source file or test is named. Start by reproducing the provided speedtest and iptables output on Ubuntu 20.04 with Docker installed and no containers, then trace which Docker networking behavior could affect forwarding; done means the upload limit is explained and the regression is covered by a reproducible test.