If you wish, you can do downgrade by special firmware version.
Ignore this "Software downgrade from WW-17.1810.1910.63 (Android Q)", it is because when it was released actual version was 63, but you can use for any A10 firmware release.
ZenFone 6 (ZS630KL) BIOS & FIRMWARE | Phone | ASUS GlobalVersion Android Q downgrade to Android P
2019/11/04
1.86 GBytes
ASUS ZenFone 6 ZS630KL Software downgrade from WW-17.1810.1910.63 (Android Q) to target Image Version: WW-16.1220.1909.194 (Android P) by using MicroSD card for WW SKU only* Please follow step 6 and ensure to backup data before downgrade.
Steps of Update:
1. Prepare a MicroSD card.
2. Check software version of your device**
3. Only apply to same SKU update, Example: WW->WW, CN->CN, TW->TW, ID->ID.
4. Software update cannot transfer the software SKU.
5. Wrong SKU may cause update failure, please update the same SKU version only.
6. How to manual update firmware please refer to
https://www.asus.com/tw/support/FAQ/1039929*How to know the device model?
Path: Settings->About-> Model number
Example: ASUS PadFone2
**How to know the device software version?
Path: Settings->About-> software information->Build number
Example: CHT_PadFone2-user-10.4.17.15-UpdateLauncher
*System upgrade may cause part of data missing, please backup your important data before system upgrading.