Low marks on Glassdoor are pretty much the norm in European tech companies, especially in countries like Germany.
Belgian news has an item every half-year where some big shot company boy complains about how difficult it is to get (good) ITers. This gets thinned down to "there's not enough ITers". Reality is that they refuse to pay for the quality employees they NEED, so those work elsewhere/leave the company/work remote.
This is the complaint every company I've worked for or met with so far has fielded at me, which is kind of hilarious as they all also unequivocally refuse to pay a reasonable wage.