Publishing to Youtube, Vimeo, Soundcloud, or any other public website is considered as commercial use even if you have never make any money from the tracks or plan to do so.
Under Copyright rules this is classed as 'Public performance' - whether you gain financially or not is irrelevant - you are 'publicly broadcasting', and therefore require the Commercial / pro licences, where available, from Catooh.com, for all soundpools used.
The Show and Discuss forum here is OK as this is a Magix provided service for users and putting your creations here is allowed.
If you use Music Maker to compose and create melodies, drum beats etc using the synthesizers ie no soundpool material then there is no problem putting your creations on to the Internet
The licensing of most Magix programs allows personal use only - public performance of any kind requires the pro licences.