Overall, the process took too much effort and in the end, I didn't get a clear feedback on why I was rejected.
I first applied online, the applicaiton online meant uploading your CV to their internal system and at the same time answering an online case-study test questions to demonstrate how you would react in certain situations, it was a multiple-choice test.
After these initial steps, they invited me to Warsaw to take the so-called "Reasoning test", which consisted of English paragragh reading questions whose sentences were placed in a "reverse" way (so the questions were hard to read&understand), math questions and logic questions, I had to leave my city and go to Warsaw just to take this exam (It wasnt possible to take it online).
After passing this exam, the next step was the face-to-face interview, for which I went to Warsaw again (at this stage they offered the option to have it over phone but I assumed that going there in person to have this interview would show them how much I take this job seriously, which turned out to be useless, so went to Warsaw yet again for nothing).
At this stage, I interviewed with a relatively old HR lady, who asked 10 questions only by looking at the paper in front of her and noting down my answers there. The questions were rather based on my previous experience (despite the fact that it was supposed to be a junior position!) and they were in the style of "what was the most challanging thing you have done?" "How did you solve an issue with your team?" etc. In spite of that, thanks to my relevant experience in my work back then, I gave answers to all of them, even providing real-case scenarious for most of them questions.
Despite all these explanations which took an hour, on the same day, I received an email saying that I was rejected, I asked for a detailed expanation but no information was shared under the pretext of "confidentiality", and they encouraged me to apply for this position in 12 months again. Yes, for a junior position, they encouraged me to re-apply in 12 months, like a joke!