BenQ firmware updates for projectors/monitors on Windows 10 typically use:
Load the scatter file into the SP Flash Tool and change the setting from "Download Only" to "Firmware Upgrade" to avoid potential bricking. Connection: Click the "Download" button in the tool , then connect the powered-off phone to the PC via USB. Some models require holding the Volume Down key while connecting to trigger detection. Confirmation: green ring or "Download OK" pop-up signifies the process is complete. BQ - John Canning
: Flashing will erase all data. Back up your files to an external source.
Since the official BQ site is gone, you can find verified stock ROMs at community repositories like the BQ-MTK Firmware Collection on GitHub SP Flash Tool : The software that performs the flash. Stock Firmware