I don't know if this will help but I had the same error and followed the same steps as you did. Additionally, if I went to Steam downloads I had a download pending for BF6 of around 500B that was stuck with the message "Game not released". To fix that, I went into Steam properties for the game, DLC tab and unchecked "Battlefield Multiplayer Marker" and "Battlefield Multiplayer HD Marker". That did not fix it but at least I had no more pending downloads.
After that I did a bunch of system reboots until finally while the game was booting up one time I used Alt+Tab and the Windows Defender Firewall dialog popped up; the one where you can allow an app to use Public or Private networks on your PC. Up until that point I did not get that dialog even though I was constantly tabbing out to check stuff in Chrome while the game was running, so I am not sure what caused it to finally show up. After allowing everything, the game was able to reach the servers. If that does not show up for you, you can try to manually allow the BF6 app in the Windows Defender Firewall and see if that solves your issue.
did that still doesn't work
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