In the ExtremeXOS 22.3 User Guide under and in the ExtremeXOS 22.3 Command Reference Guide under the configure forwarding switching-mode command.
xos0070817
Add the following information:
Cut-through forwarding mode is supported only on the 40G ports of the Summit X770, X670-G2, and ExtremeSwitching X870, X690 series switches; and the 100G ports of the ExtremeSwitching X870 and X690 series switches.