The address of 0x00100/00101 is LINK_BW_SET/LANE_COUNT_SET register in DPCD
The LINK_BW_SET and LANE_COUNT_SET registers are involved in training of the upstream link so are contained in the DP 1.2 Repeater. All accesses to this register are to the DP 1.2 Repeater and are not passed downstream. The write data is indirectly passed to the downstream device as a result of the training of the downstream link, i.e. repeater trains downstream link to same configuration as upstream link.