WINDOWS 11 AUTOMATICALLY update bios 1.1.31 for xps 8930 !?

The newest BIOS on the 8930 Support page is 1.1.30 so this may be a new release. Manufacturers do, at times, release such upgrades to MS. But I am not a fan of such updates and would only suggest Dell updates instead of a Windows update to the BIOS. And even then if the system is working well and the BIOS update does not address a specific problem you may be having, then let well enough alone.

To avoid automatically BIOS update, you need to disable UEFI Firmware Capsule Updates in BIOS settings.