Newer devices (Dimensity 700, 800, 900 series) have the Kamakiri exploit patched. In that case, you need an MTK Auth Bypass Dongle (Easy JTAG, Medusa Pro, or MRT Dongle).
Recent Oppo and Realme security patches have made entering the older "BROM" (Bootroom) mode more difficult. Consequently, modern repair tools now rely heavily on Preloader Mode to bypass these restrictions for tasks like FRP removal or bootloader unlocking. Essential Drivers for Oppo and Realme
Yes, on many OPPO/Realme, simply connect the phone to a PC with a deep-discharged battery. It will fall into Preloader mode waiting for charge.