Yes, came from totally stock CN 12.5.2 to EU 12.5.4.
No, didn't check for slot a or b, I read the post from a page up and decided to trust that it was all written in the code. Followed the instructions and video and it worked just as it was supposed to.
I have been patiently waiting for 7 days for my first Xiaomi device (11U) to have it's bootloader unlocked and today is finally the day.
I haven't flashed anything since I was using the original OnePlusOne as my daily driver, so wish me luck.
I've been studying this forum during my waiting...