In MAX14690 design, are there any other ways to disable internal Bucks and LDOs except through I2C to configure registers?

They can be controlled through the MPC_ inputs if LDO1En default value is 10 or 11.

         LDO1En[1:0]
                 LDO1 Enable Configuration (effective only when LDO1Seq = 111)
                 00 = Disabled – LDOs OUT not actively discharged unless Hard-Reset/Shutdown/Off Mode
                 01 = Enabled
                 10 = Enabled when MPC0 is high (regardless of MPC1)
                 11 = Enabled when MPC1 is high (regardless of MPC0)