How big can a rocky planet get?

Basically title. How large could a rocky planet get? What composition would help maximize size while maintaining rocky planet status?

Is there a point where the gravity creates enough pressure at the core to start fusion? I know that iron would concentrate in the core and won't fuse so maybe this isn't possible unless somehow it had almost no iron.

Is there a point where it's too big for gravity to hold on to new heavy material? That might be a silly thing to say, I'm just going by the ratio of M/(r^2).

Would it inevitably turn into a gas giant? Maybe assume little-to-no atmosphere.

Just a hypothetical that popped up in my head.