Question about subtitles and capitalization

According to the title formatting guide (https://help.imdb.com/article/contribution/titles/title-formatting/G56U5ERK7YY47CQB?ref_=helpsrall#), Dutch (and other) titles should only capitalize the first word of a title and exceptions like names. There is also a section about subtitles where it says they are separated from the main title. The guide also states that a subtitle can be seen on another screen than the main title. To me, these two things suggests that for Dutch (and other) titles, the first word of the subtitle should also start with a capital letter, but it's not clearly/explicitly stated in the guide. So, is my assumption correct? (FWIW, I personally feel it looks better if the first word of the subtitle starts with a capital letter). An example might make my question more clear: Should this title (https://www.imdb.com/title/tt30784359/reference/) be listed as De club van Sinterklaas film: Het grote sneeuwavontuur or as De club van Sinterklaas film: het grote sneeuwavontuur? (Sinterklaas is the name of the main character and should therefore start with a capital letter).