That would be totally illegal in Germany, and most of the EU. Not only the employee tracking and forcing them to install anything on their private devices, but also the data collection and not disclosing what is collected, where, and how long, and not implementing an automatic deletion.
Here in the UK government introduced zero rights employment just few days ago and that would be totally legal here.
I am resolutely not a fan of our current UK government and they will certainly work to weaken worker's rights, but (absent of any corroberating references) this is just BS.