3GPP 38.300 v19.3.0 — the document's own text
16.9.2.3 RLC
The services and functions of the RLC sublayer as specified in clause 6.3.2 are supported for sidelink. TM is used for SBCCH. Both UM and AM are used in unicast transmission while only UM is used in groupcast or broadcast transmission. For UM, only unidirectional transmission is supported for groupcast and broadcast.