How can I upgrade Windows 10 to Windows 11 25H2 without data loss?

About your question of upgrading Windows 10 to Windows 1125H2. Older hardware, like your Intel Core i7-6800K and GTX 1070, may encounter driver compatibility issues, potentially leading to stability problems, reduced performance, or device malfunctions. Some older or less common programs might not be fully compatible with Windows 11, which could cause crashes or require updates.

Windows upgrades can sometimes introduce bugs or stability issues, especially on systems that are a few generations old or have complex configurations. Some users experience system crashes, freezes, or unexpected behavior after upgrading. 

While upgrading Windows 10 to Windows 1125H2 without data loss is possible and often successful, these potential disadvantages highlight the importance of proper preparation. If your hardware and software are compatible and you take backups, the risks are minimized. However, be aware of possible stability, performance, and compatibility issues, especially given your hardware's age relative to Windows 11’s system requirements.