is it only for new users of the Galaxy client or can anyone claim it? Having used Galaxy for quite some time I don't see any means to claim it within the application
do I need to join the Galaxy 2.0 beta? My version number is 2.0.44

See if this helps: https://www.gog.com/forum/general_beta_gog_galaxy_2.0/game_giveaway/post2

it didn't help, but thanks for trying