I lived in Minsk and only now I have corrected myself and went inside thanks to an online quest-guided tours from my phone)
I took a quest tour on whatiftour com (Secrets of Skaryna: The search for unique UNESCO houses on Independence Avenue) and finally visited the main post office. Inside, you can examine the stained glass windows, the chandelier also attracted attention and drew attention to some elements thanks to the quest.
I also went to the "boutique" for philatelists for the sake of interest, it was interesting to look at the stamps issued by year.
I recommend you to visit for a variety of walking experience in Minsk.
I also recommend trying the quest tour, you will learn a lot of informative facts in the process.