The Bertelsmann Foundation wants to promote social integration and diversity. It advocates for creating a "comprehensive and long-term migration architecture" for Germany. - https://en.wikipedia.org/wiki/Bertelsmann_Stiftung#Society

But as the sibling comment notes, in other areas they're not at all left-leaning, e.g.:

Arvato, a division of the Bertelsmann Group, declared the privatization of public services a strategic business area.

It should not surprise anyone that characterizing their politics on a one-dimensional left-right spectrum is inaccurate (findings such as https://arxiv.org/abs/1904.12320 notwithstanding).

That doesn’t really make them left-leaning. With the same argument the CDU would be a left-leaning party.

A tempting conclusion if you look at Germany’s transformation since the war. But what does left-leaning even mean.

Before Occupy Wall Street went down in flames, (actual, hard) leftist liked to critique the false dichotomy between what’s presented as left-wing and right-wing politics in western democracies, and they were very right to do so. What I wrote here about media applies to politics just as well: https://news.ycombinator.com/item?id=28904146