Being a minor, Mikołaj in 2019 obtained family court permission, thanks to which he was able to establish the Foundation for the Student Rights [Fundacja na rzecz Praw Ucznia]. Hence, since November 18th 2019, he has been its president. The Foundation undertakes educational as well as intervention and counseling activities within the framework of its activities.

When it comes to the first branch, the Foundation has been organizing the Student Rights Knowledge Olympiad since its beginnings (in its first edition in the 2019/2020 school year as a competition, from 2020/2021 as an Olympiad), with Mikołaj as the chairman of the Main Committee and the chief organizer. In the 2023/2024 school year, schools from all over Poland registered 705 students for the first stage of the Olympiad. Its organization was supported by, among others: Speaker of the Sejm [first Polish parliamentary chamber], the European Commission Representation in Poland, the Ombudswoman for Children, the Supreme Bar Council, the National Council of Bailiffs and the Chairman of the Committee of Legal Sciences of the Polish Academy of Sciences. In addition, honorary patronage was granted by the Minister of Education.

In addition, Mikołaj regularly gives lectures, speeches and training sessions on the topic of the student rights and duties. Examples of venues where they have been delivered are: Warsaw (at the order of the Warsaw City Hall), Poznań, Oborniki Wielkopolskie (and surrounding villages), Radomsko, Krzyżowa or Bolewice. In March 2024, at the invitation of the Ombudswoman for Children, Mikołaj gave a webinar on her Facebook page on student rights and duties, as well as on how to protect the rights at school.

The Foundation's intervention and counseling activities include regular assistance to all those who turn to the Foundation with problematic situations taking place in their schools (or their children's schools). The Foundation receives several hundred requests for assistance each year.

Morevoer, in 2021, Mikołaj became the observer on behalf of the Foundation to Child Rights Connect, a Geneva-based organization that provides substantive and administrative support to the UN Committee on the Rights of the Child. In March 2024, the Minister of Education appointed Mikołaj to the Student Rights and Duties Advisory Team, which aims to prepare a bill reforming this matter and preparing the legal basis for the functioning of the future nationwide Student Ombudsperson.

In 2017, he was the Speaker of the XXIIIrd session of the Children and Youth Sejm [Sejm Dzieci i Młodzieży; Sejm is Polish first parliamentary chamber]. From 2018 to 2022, the co-organizer of the Young People's Parliament of the Republic of Poland (in its first edition called the Parliament of Children and Youth, initiated as a result of the cancellation of the XXIVth session of the Children and Youth Sejm in 2018). Moreover, he is the founder and former managing editor of the "Gazeta Kongresy" — a youth magazine published monthly.

From February 2022 to June 2023, he worked at the Short-Term Shelter Point for Ukrainian Refugees run by the City of Warsaw — firstly as a volunteer, from May 2022 as a full-time employee of the Warsaw Crisis Intervention Center, mainly on the night shifts (to combine the work with his Foundation and two degrees). The point ended its activity at the end of June 2023 due to the corresponding decision of the Warsaw's City Hall. During its operation it welcomed more than 7,000 people in war crisis.