Since the time of Android Marshmallow, Google introduced Adoptable Storage, however, many of the OEM restrained from providing the feature. But, now Samsung will bring this feature along with Android Pie.
A member of XDA found this feature on his Note 9 Android beta builds. After he inserted his microSD card into the device, he was welcomed to the Android Adoptable Storage screen.
Adoptable Storage allows you to use the microSD card as a part of internal storage or standard external storage. if you select the first option, you can use the sd card as internal storage, therefore, can install apps, games to SD card. However, once you select the first option, you cannot use the SD card in other devices.
But if selecting the second option, You can use the card with other devices as well.
Right now, the feature isn’t working. But, since its availability, we are sure that this feature will find its way into official builds.
Source: Android Police