Why My PC can't be upgraded to Windows 11 25H2?

The "23H2" version was the last to officially support your 7th-gen CPU with bypass methods. Starting with 24H2, Microsoft implemented a stricter hardware compliance check that is much harder to bypass for updates, which is why you can't upgrade to Windows 11.

You likely installed 24H2 using one of the bypass methods (like a registry edit or using a Media Creation Tool at the time which was less strict). Microsoft has now closed many of those loopholes for the in-place upgrade from 24H2 to 25H2 via Windows Update. Since the standard Windows Update path is blocked, you will need to use a clean installation method. Recommend: Use a Third-Party Tool.

1. Download the Windows 11 25H2 ISO file and the professional third-party software.
2. Run software, select your USB drive, and select the downloaded ISO.
3. A new window will appear. In the "Windows User experience" section, It has checkboxes to "Remove requirement for an online Microsoft account" and, most importantly, "Remove requirement for 4GB+ RAM, Secure Boot and TPM 2.0". Ensure this second box is checked.
4. Proceed to create the USB. When you boot from it, the hardware checks will be automatically bypassed.

Installing Windows 11 on unsupported hardware is considered an "unsupported" scenario by Microsoft. While it generally works fine, there is a non-zero chance that a future update could fail or cause instability. Your i5-7400 and 16GB RAM are perfectly capable of running Windows 11 well, so this is a relatively low-risk procedure if you can't upgrade to Windows 11 25H2, but it's crucial to be aware of the caveat.