You’re totally right about options. I was thinking more explicitly about stock itself (e.g. RSUs in the case of employees at companies that issue those instead of options, or founder's stock in my personal case).

Separate from that, things are still more fraught in Germany: whatever your US taxation situation is, I'm not aware of any situation where a valuation change in stock/options/etc you're holding will trigger a taxable event for you, as I understand to be the case with Germany. As I understand equity taxation in the US, you'll only ever be taxed when events happen that you yourself have initiated (e.g. exercising options or selling stock).