Sorry my English is bad so I don't know how to answer your questions clearly. I just went to https://mifirm.net/model/venus.ttt#eu and downloaded the eu fastboot rom V12.5.7.0.RKBCNXM and did 8 steps digeratz mentioned above:
"Step 1. I've downloaded old fastboot EU rom (I've used May 13, 2021...