If nothing works, I would try to flash an official rom version via Miflash without relocking the BL and from there try to flash xiaomi.eu again the way you did.
No idea what went wrong on your side @dudex , so after the script was successful, it should automatically reboot into the system. You did the right step. Your attached log seems correct to me, maybe try to flash it again and see what happens.
I agree with you on the part with being a bit laggy after rebooting and also the sliding down the control center sometimes is a bit sluggish. Unfortunately the devs do not own this device and cannot do much for that reason. Apart from that I had never issues with calls or any system apps.
It is not possible to unlock it officially, unless you try to contact someone on Telegram who offers a paid service but from what I have heard, even that is not possible on a few devices anymore. Of course there are also scammers concerning this topic, be careful.