Dear DanuwatChutayothin-6083,
The new ISO file name you provided shows the problem: ...CLIENT_IOT_LTSC_EVAL_...
Your "About" screen confirms this: "Windows 11 IoT Enterprise LTSC 2024 Evaluation"
This is the source of the activation failure. You have installed an Evaluation (trial) version of Windows from the Microsoft Evaluation Center. These versions are for temporary testing (usually 90 days) and cannot be activated with a permanent OEM or retail product key.
The product key on your Dell sticker is a permanent OEM license. The software you installed is a temporary Evaluation license.
The keys for these two different licensing channels are not interchangeable, which is why the slmgr command is failing with error 0xC004F069 (key mismatch).
To resolve this, you must perform a clean installation.
You cannot use the ISO from the public Microsoft Evaluation Center. Since you purchased the PC and the license from Dell, you must obtain the official Dell OEM installation media for "Windows 11 IoT Enterprise."
Please contact Dell Support or log in to your Dell OEM/Volume License portal to download the correct, non-evaluation ISO file that corresponds to the license you purchased.
Once you reinstall Windows using the correct Dell OEM media, the product key on your sticker will be accepted, and your system will activate correctly.
If this clarifies the new path forward, please click "Accept Answer" below. This helps other members of the community who might run into this "Evaluation" vs. "OEM" license issue.