Complex sentence: Music was the least restricted cultural activity, probably because Hans Frank considered himself a fan of serious music; he eventually ordered the establishment of the Orchestra and Symphony of the General Government in its capital, Kraków.
Split into simpler sentences: Music was the least restricted of cultural activities, most likely because Hans Frank regarded himself as a fan of serious music. In time, he ordered the creation of the Orchestra and Symphony of the General Government in its capital, Kraków.