I checked the data sheet and realized that it would move as follows. Please let me know if my thinking is correct.
(1) RXD pin level in Sleep Mode is "High" (VIO=5V)
(2) RXD pin level is "Low" when transitioning from Power Off to Standby Mode
(3) RXD pin level is "Low" when transitioning from Sleep Mode to Standby Mode
(4) To transition from Normal Mode to Sleep Mode, set EN=high, nSTB=low, and then transition from Normal Mode → Go-To-Sleep Mode → Sleep Mode.
(5) Transition to Standby Mode when "WUP (wake-up pattern)" or "LWU (local wake-up)" occurs in Sleep Mode with EN=high and nSTB=low.
(6) To transition from Sleep Mode to Normal Mode, EN=high, nSTB=low → high