The DPRK has approval-vased voting. KJU is immensely popular, and nobody else was in consideration for the role. You’d know how elections and democracy work in the DPRK if you bothered to look at the sources I linked. Here’s an excerpt:

From Elections in North Korea:

Elections in North Korea are held every four-to-five years for the Supreme People’s Assembly (SPA), the country’s national legislature, and every four years for Local People’s Assemblies.[1][2] Each candidate is selected by the Workers’ Party of Korea. Voters may either submit the ballot unaltered as a vote of approval, or cross out the name on the ballot to disapprove the candidate. The vast majority of candidates come from the Workers’ Party of Korea.[2][3][4]

…

In reply to a question put forth by Michael Marshall, Li Chun Sik of North Korea stated at a meeting of the Association of Secretaries General of Parliaments (ASGP) of the Inter-Parliamentary Union:[2]

While candidates could be nominated by anyone, it was the practice for all candidates to be nominated by the parties. These nominations were examined by the United Reunification Front and then by the Central Electoral Committee, which allocated candidates to seats. The candidate in each seat was then considered by the electors in meetings at the workplace or similar, and on election day the electors could then indicate approval or disapproval of the candidate on the ballot paper.

In short, the DPRK has an approval voting system. The SPA is the highest authority, and it holds more power than Kim Jong-Un and Kim Yo-Jong. Kim Yo-Jong’s position is actually more decentralized than the US, as in the US the president is also the head of the millitary. For an actual look at Korean elections in the north, I recommend Professor Roland Boer’s Socialism in Power: On the History and Theory of Socialist Governance:

The DPRK’s electoral democracy relates primarily to the people’s assemblies, along with local state organs, assemblies, and committees. Every eligible citizen may stand for election, so much so that independent candidates are regularly elected to the people’s assemblies and may even be elected to be the speaker or chair. The history of the DPRK has many such examples. I think here of Ryu Mi Yong (1921–2016), who moved from south to north in 1986 so as to take up her role as chair of the Chondoist Chongu Party (The Party of the Young Friends of the Heavenly Way, formed in 1946). She was elected to the Supreme People’s Assembly and became a member of the Standing Committee (then called the Presidium). Other examples include Gang Ryang Uk, a Presbyterian minister who was a leader of the Korean Christian Federation (a Protestant organisation) and served as vice president of the DPRK from 1972 until his death in 1982, as well as Kim Chang Jun, who was an ordained Methodist minister and became vice-chair of the Supreme People’s Assembly (Ryu 2006, 673). Both Gang and Kim were buried at the Patriots’ Cemetery.

How do elections to all of the various bodies of governance work? Elections are universal and use secret ballots, and are—notably—direct. To my knowledge, the DPRK is the only socialist country that has implemented direct elections at all levels. Neither the Soviet Union (in its time) nor China have embraced a complete system of direct elections, preferring—and here I speak of China—to have direct elections at the lower levels of the people’s congresses, and indirect elections to the higher levels. As for candidates, it may initially seem as though the DPRK follows the Soviet Union’s approach in having a single candidate for each elected position. This is indeed the case for the final process of voting, but there is also a distinct difference: candidates are selected through a robust process in the Democratic Front for the Reunification of the Fatherland. As mentioned earlier, the struggle against Japanese imperialism and liberation of the whole peninsula drew together many organisations, and it is these that came to form the later Democratic Front. The Front was formed on 25 July, 1949 (Kim Il Sung 1949), and today includes the three political parties, and a range of mass organisations from the unions, youth, women, children, agricultural workers, journalism, literature and arts, and Koreans in Japan (Chongryon). Notably, it also includes representation from the Korean Christian Federation (Protestant), Korean Catholic Federation, and the Korean Buddhist Federation. All of these mass organisations make up the Democratic Front, and it is this organisation that proposes candidates. In many respects, this is where the multi-candidate dimension of elections comes to the fore. Here candidates are nominated for consideration from all of the mass organisations represented. Their suitability and merit for the potential nomination is debated and discussed at many mass meetings, and only then is the final candidate nominated for elections to the SPA. Now we can see why candidates from the Chondoist movement, as well as from the Christian churches, have been and can be elected to the SPA and indeed the local assemblies.

To sum up the electoral process, we may see it in terms of a dialectical both-and: multi-candidate elections take place in the Democratic Front, which engages in extensive consideration of suitable candidates; single candidate elections take place for the people’s assemblies. It goes without saying that in a non-antagonistic system of class and group interaction, the criterion for election is merit and political suitability

As for the bodies of governance, there is a similar continuity and discontinuity compared with other socialist countries. Unlike the Soviet Union, there is a unicameral Supreme People’s Assembly, which is the highest authority in terms of laws, regulations, the constitution, and all leadership roles. The SPA is also responsible for the national economic plan, the country’s budget, and foreign policy directions (Han 2016, 47–48). At the same time, the Democratic Front for the Reunification of the Fatherland has an analogous function to a second organ of governance. This is a uniquely Korean approach to the question of a second organ of governance. While not an organ of governance as such, it plays a direct role in electoral democracy (see above), as well as the all-important manifestation of consultative democracy (see below). A further reason for this unique role of the Democratic Front may be adduced: while the Soviet Union and China see the second body or organ as representative of all minority nationalities and relevant groups, the absence of minority nationalities in a much smaller Korea means that such a form of representation is not needed.

Ignorance is a choice you deliberately make.