You can't subscribe to topics, only make them favourites for easier access. Click on #gamedev and then click the star (using peakd). After that you find the topic in favourites.

There are two general communities. Gamedev and game development. Gamedev is not active and creator not an active user anymore. Game development is active and found here created/hive-176981

When writing a new post it is in general best to post it in a community for most exposure. Using peakd you can also crosspost to your own blog at the same time if you want.