The Sidemen charity match has been held on six occasions since its inception in 2016. These matches have taken place at various stadiums, including St Mary's Stadium, the Valley (three times), London Stadium, and Wembley Stadium. The charity matches are played between Sidemen FC and the YouTube Allstars, and they are live-streamed on YouTube to raise money for various British charities.

Summary of key points:

• Total Sidemen charity matches held: 6
• Venues: St Mary's Stadium, the Valley (3 times), London Stadium, Wembley Stadium
• The matches feature Sidemen FC vs. YouTube Allstars
• These matches raise money for charities and are livestreamed on YouTube.

This answers the question about the number of Sidemen charity matches as of now.