Cannot get into fastboot

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Greetings smart people,

I just got this redmi9 from my brother. Phone is usable at the moment.

I want to:
1. Unlock bootloader
2. Flash Twrp + rom

My problem is i cant get the phone to enter fastboot mode (bootloader hasn't been unlocked yet). While the phone turned off, holding voldown + power button, will not go into fastboot, it will just reboot back to miui.

Is this softbricked or something?

Please and TQ.