3GPP 38.300 v19.3.0 — the document's own text
16.23.5.4.2 Segmentation
A D2R upper layer data SDU except for inventory response can be segmented in A-IoT MAC layer so that the size of the D2R Upper Layer Data Transfer message is equal to the scheduled TB size.
Segmentation of R2D upper layer data SDU in A-IoT MAC layer is not supported.