They do little to no anti competitive behaviour, clutching at straws would be that they require you to keep price parity on steam keys (except on sales).
It is very much not clutching at straws to claim that. That policy is a major element of the Wolfire v. Valve case. You can also look at how despite charging a 12% platform fee, Epic Games Store does not sell games 18% cheaper.
It’s an abuse of Steam’s established market share and consumer habits to coerce publishers into not offering consumers a fair price on other platforms. It very literally stops EGS from competing on price, which is pretty much the only area where Epic can beat out Steam, since Steam otherwise is much more convenient, provides more functionality, and has more community-generated content (i.e. workshop material).
It’s hard to say that isn’t anti-competitive, especially because such a policy is only effective due to Steam’s existing market share.
Epic literally does anti competitive things like exclusivity and taking games they have some stake in off other store fronts or crippling their functionality.