For the MT6765 chipset, you cannot use versions older than due to changes in DA (Download Agent) and security authentication (SECURITY BOOT / SLA/DAA).
"SP_Flash_Tool_v5.2128_Win.zip site:github.com" sp flash tool mt6765 link
These devices often have and DA (Download Agent) restrictions. Hence, a generic SP Flash Tool might fail. You need the MT6765-dedicated DA file and a compatible tool version. For the MT6765 chipset, you cannot use versions