fastboot set_active command does not exist

fastboot change slot
➡️【Mk.com】✅भाग्यशाली महसूस कर रहे हैं? ✅कैसीनो ✅2,200 स्लॉट मशीनों, 100 से अधिक गेमिंग टेबल, 30-टेबल पोकर रूम और लाइव मनोरंजन के साथ अंतहीन मनोरंजन प्रदान करता है...✅ 

I managed to set slot A active with no further change and am now struggling to set slot B active fastboot --set-active:a fastboot

Hi fellow OP6T users, is there a way to change the boot slot for example from _a to _b within the fastboot mode? I read something about a

fastboot set active slot Fastboot firmware, ZIP firmware is official from Xiaomi EU ROM, TWRP and Card slot microSDXC Internal 64GB 4GB RAM, 64GB 6GB RAM

fastboot get active slot I managed to set slot A active with no further change and am now struggling to set slot B active fastboot --set-active:a fastboot