federal chancellor
Specifically refers to the head of government in a federal system, most commonly the German Bundeskanzler or Austrian Bundeskanzler. Not a generic term for prime minister.
The federal chancellor of Germany is Olaf Scholz.
The federal chancellor is elected by the federal parliament.
首相 is a general term for prime minister, while 連邦首相 specifically denotes the chancellor in a federal state.
大統領 is a president, typically the head of state, whereas 連邦首相 is the head of government in a federal parliamentary system.
Compound of 連邦 (れんぽう, 'federation') and 首相 (しゅしょう, 'prime minister').