I first found this here: https://www.ettoh.jp/
Does this mean the drink is easy to drink? Or that it's meant to be drunk in a carefree setting? One example I was taught for 気楽 is in 気楽なパーティ (informal party).
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気楽な corresponds to 気が楽 and describes feeling at ease or relaxed, a semi-literal translation of the latter might be "ease of mind".
"Easy" itself has several meanings in English, and "easy to drink" would not necessarily be interpreted as meaning the opposite of "technically difficult to drink".
In any case, translating 気楽なお酒 as an "easy drink" would be better than "a drink supposed to be drunk in a carefree setting".
But really, 気楽なお酒 is just associating "ease of mind" with "drink". It's certainly not about the technicalities of whether it's easy to swallow, but also not about whether it's meant to be drunk in a certain setting. It's just a drink that they want you to associate with a relaxed situation.