I use nftables to set my firewall rules. I typically manually configure the rules myself. Recently, I just happened to dump the ruleset, and, much to my surprise, my config was gone, and it was replaced with an enourmous amount of extremely cryptic firewall rules. After a quick examination of the rules, I found that it was Docker that had modified them. And after some brief research, I found a number of open issues, just like this one, of people complaining about this behaviour. I think it’s an enourmous security risk to have Docker silently do this by default.
I have heard that Podman doesn’t suffer from this issue, as it is daemonless. If that is true, I will certainly be switching from Docker to Podman.
Cockpit definitely has the ability to create bridge devices. I haven’t found a tutorial specifically for cockpit, but you can follow something like this and apply the same principles to the “Add Bridge” dialog in Cockpit’s network settings.