So I'm actually German but haven't been back home in 5+ years, except for a short business trip where I didn't really do all that much.
Now I'm going back for a few weeks almost exclusively for touristy purposes (my wife has never been to the EU), and I'm wondering what's really changed / what is considered must-haves these days?
Not Germany specific, but if you need an eSim for mobile phone service while you’re here visiting, I would recommend Airalo. Really good prices for a temporary SIM (e.g. $10 USD for 3GB) and no need to go through the hassle of registering and activating a SIM card.
I still hold on to my German sim, so that's not a problem. And unfortunately eSIMs are banned in China since you can just download any random one and bypass the great firewall, so our phones are restricted to physical ones :-/
For one, the DB Navigator app is a real multitool about most things public transport, even if you are not taking high-speed trains. You can use it instead of most local official apps.