Xiaomi has recently shared a list of some of its selected devices on the official website, so that if you are using a Xiaomi smartphone model from the list given below, then you can easily increase the RAM of your device by using the RAM extension feature.
List of Xiaomi RAM extension updated list 09 December 2021
REDMI Devices
Redmi K30
Redmi Note 10 Pro 5G
Redmi 10X 4G
Redmi 10X 5G/Pro
Redmi K30 5G
Redmi K30 Ultra
Redmi 10
Redmi Note 8
Redmi 9T
Redmi Note 9 5G
Redmi Note 9T
Redmi K40
Redmi Note 10 Pro
MI Devices
Mi 11 Ultra
Mi 11i
Mi 10
Mi 10 Pro
Mi 10 Ultra
Mi MIX 4
Mi 10T Lite
Mi 10 Lite Zoom
Mi 11
Mi 11 Pro
All Snapdragon 888, 870, & 865 Phones (except Mi MIX Fold as it is yet to get MIUI 12.5)
POCO Devices
POCO F3
POCO X3 GT
POCO X3 NFC