After a 4K license is loaded for the TX50, the maximum codec capability queried in the system information is still 1080p60.
TX50 software version: V500R002C00SPC600
Upgrade the TX50 to V600R006C00SPC300 and load the license again. The maximum codec capability becomes 4K. The problem is solved.
Summary: The TX50 does not support the 4K codec capability in the V500R002C00 version. Only a version later than V600R006C00 supports the H.265 4K codec capability. After the H.265 4K*2K capability is enabled, the TX50 cannot be downgraded to V500R002C00.