I have written a guide on how to downgrade Huawei phones to previous EMUI versions. If I am missing any method that is more efficient in downgrading feel free to comment. :
Free Remove Frp Huawei Mate 20 Pro LAYA-L29C 9.1.0 DOWNGRADE
Huawei mate 20 Pro Downgrade from 10 to 9 done | Martview-Forum
Huawei P40 Pro Install GSM EMUI 11 Downgrade EMUI 10 | Downgrade with Hisuite proxy NOT WORK - ICTfix | Huawei, Samsung galaxy phone, P40
Huawei Mate 20 Pro (LYA-L29) downgrade to 9.1 · Issue #151 · ProfessorJTJ/HISuite-Proxy · GitHub
Huawei Mate 20 Pro - Full Frp Downgrade File Android 10 LYA-L29/LYA-L09 - Gsmedge Android ERROR 404 - Gsmedge Android
Downgrade File For LYA-L09 FRP Bypass Huawei Mate 20 Pro