Deoxys had its first debut as a raid boss in the EX Tier raids globally, back in October 1st 2018. It however, would not be available shiny until it returned to Tier 5 raids during the Enigma Week event back in August 2020. Even if you caught one earlier, the Deoxys could not be transferred to the main series games until the HOME v2.0.0 update, which supports Brilliant Diamond & Shining Pearl. For this file to be transferable across games without any stats oddities, you cannot