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My guess is that this is an anti-cheat problem. The symptom of those is often everything working on Linux except the multiplayer, with no explanation.

I don't play Titanfall 2, but apparently it uses Easy Anti Cheat. EAC and Valve Anti Cheat are two very common ones. Usually, VAC is considered restrained and Linux friendly, while EAC is more aggressive (borderline rootkit). Since Linux is designed to have security against malware, it's hard to get EAC to work right on it.

Commercial launchers like Steam or Epic Game Store can sometimes include some black magic to placate the anti-cheat, so the game works on those but not with third party launchers like Lutris. So that's worth a try. You could also try asking the developer for support, they should at least be able to confirm whether it's the anti-cheat causing the issue.

According to ProtonDB it should run, though: https://www.protondb.com/app/1237970/