https://makecode.adafruit.com/reference/pins/i2c-write-register
shows that the MakeCode block has 3 parameters but its JavaScript has 4. The "valueFormat?: NumberFormat" Javascript parameter is missing from the MakeCode block. A workaround is to manually add it to the JavaScript and then go back to Blocks (where 6 lines of JavaScript are shown in a block) but it should be part of the MakeCode block like it is for the "i2c write number" block.
https://makecode.adafruit.com/reference/pins/i2c-write-register shows that the MakeCode block has 3 parameters but its JavaScript has 4. The "valueFormat?: NumberFormat" Javascript parameter is missing from the MakeCode block. A workaround is to manually add it to the JavaScript and then go back to Blocks (where 6 lines of JavaScript are shown in a block) but it should be part of the MakeCode block like it is for the "i2c write number" block.