I finally found the solution by changing the device tree about uart3 tx.
P9.21 uar3 rx P9.22
Verified mode change from 14 to mode 1. it is working as /dev/ttyS2
pin 241 (PIN241) 4a0037c4 00000001 pinctrl-single
pin 240 (PIN240) 4a0037c0 00060001 pinctrl-single
Thanks
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