Question about Samsung Galaxy Tab A8

What does external mean? From the internal memory point of view, the SD card is also external.
From the 2021 model onwards, 1 TB SD cards can be used, previously the maximum was 256 GB.
Sticks/hard drives of any size can be connected via USB, as long as they use an Android-supported file system; with mechanical hard drives, the hard drive must also be supplied with external power.