Hello there! Nice question indeed but let shed some light first to clarify whole procedure that is usually related to beam management.
-gNB sends TCI states (up to 64 for PDCCH, 128 PDSCH)
-It also configures an aperiodic (AP) CSI-RS (nzp/CSI-IM) with “reportquantity” configured to L1-RSRP (for instance).
a “CSI Request” field is flagged in DCI to trigger AP CSI-RS.
After that, the UE reports L1-RSRP based on aperiodic offset list (for instance), if there is only CSI on PUSCH it will follow another rule.
the gNB sends a MAC-CE command to activate a specific TCI state or a down-select (8 out of 128 relation for PDSCH, for instance) from the the list of TCI state sent previously (step 1).
A TCI field (3bits) could select one out of 8 TCI states sent by MAC-CE (step 4). This step requires that “tci-PrensentInDCI” to be sent previously (step1).
obs.: TCI state might be related to CSI-RS or SSB.
So MAC-CE activates(changes) CSI-RS/SSB, but do not trigger CSI-RS reporting for L1-RSRP.
DCI can trigger CSI-RS for L1-RSRP reporting. The resources available for L1-RSRP are configured through RRC and how they should be reported as well.
obs.: this procedure could also be periodic without need of DCI triggering.