Currently Mi Band 8 (China Version) only work with Mi Fitness app. You can't transfer old data from Zepp Life to Mi Fitness if you are not in china region because of

I've been using Mi Band 8 for a week now - AMA : r/miband

Xiaomi Mi Band 6 review: A clear winner - Android Authority

Xiaomi Global Home

Zepp Life (Formerly MiFit) on the App Store

Xiaomi Mi Smart Band 8 (Global Version) Health & Fitness Tracker with 60Hz Refresh Rate 1.62 AMOLED Display, 16-Day Battery Life, 150+ Sports Modes, Blood Oxygen, Heart Rate,Sleep & Stress Monitoring

Zepp Life App vs Mi Fitness App - kosaLife

Mi Fitness Archives - kosaLife

Export data from Zepp Life to Mi Fitness (Redmi Watch 3 & Vivo)

Mi Fit changes Zepp Life and brings more news