I'm not a historian but i was born and raised in the GDR (a.k.a east germany). The GDR really did all it could to stifle religion and get people out of the church. At least in the later years it was more passively discouraging people from going to the churches then actively suppressing the church on a large scale.
The GDR still had plenty of churches and the religion was not suppressed officially. It didn't get much (any?) state support though. If there was a chance to get rid or a church building it was usually taken. The church of our lady in Dresden was left in ruins after ww2 for 40 years. The state didn't really want to build or rebuild new churches. The state also often found reasons to get rid of existing churches (https://en.wikipedia.org/wiki/Paulinerkirche,_Leipzig) Yet sometimes if it fit the state and it did not see your religion as a threat it would also allow you to build a new church (https://en.wikipedia.org/wiki/Freiberg_Germany_Temple)
The official church had their organizations in the GDR. They could gather and of course they were infiltrated by the state security (STASI) to a certain degree. Manfred Stolpe for instance who became governor of Brandenburg after the reunification came from those circles and supposedly had STASI contacts. The church it seems had to a large degree given in to the state in order to carve out a small niche for themself. Not the entire church though. Smaller local communities were also hosting environmental activists, even punk concerts much to the dismay of the state officials and always closely observed by the state security. Often they had little backup from the church officials. The state always feared those small hard to control groups that gathered in rooms provided by local churches. Eventually it would grow to an enviromnental movement and into the "New Forum" (https://en.wikipedia.org/wiki/New_Forum) which became the most known organization to channel the discontent of the east germans into the large scale protests that would eventually bring down the regime in 1989.
Here are a few other points why religion did not play a big role in the GDR: * It was really easy to get out of the church. Just go to the registration office and say you don't wanna be a member of the church anymore and be done with it in 15 Minutes. * Religion did not play any role in public education since it is at odds with marxist ideology. There was never a question that there is no god. Religion was seen as something that needs to be overcome for the greater good of the people. * Sometimes it was really hard to be religious and still participate in society. Lets say you were in school and all your friends joined the youth organization ("Jung Pioniere" https://en.wikipedia.org/wiki/Ernst_Th%C3%A4lmann_Pioneer_Organisation). If you came from a religious backround your parents may not allow you to join. Suddenly you are the only kid in class not being able to participate in activities organized by this organization. Like sports events or short trips. Most of those were fun and you would have been left out. Most parents did not want their kids to be left out and and finally allowed them to join. * Being in the church and sticking to your principles could bring you disadvantages like not being allowed to study. If you declined military service and became a construction soldier instead (https://en.wikipedia.org/wiki/Construction_soldier) your career was pretty much over before you even started it. * In the eyes of the state and many of the people the church did not have to offer much. The state was running all the hospitals, schools and most of the welfare anyway. Why did you want to join the church? It only brought you disadvantages in your career and education.