The transmission fluid change is also time specified. Those of us with a 2018 Clarity are getting the maintenance minder messages (3) to replace the transmission fluid. As MrFixit says in a previous message, the Clarity has some wet clutches (direct engine drive for example) which can lead to debris in the fluid. Also, the additives (extreme pressure, anti-corrosion, etc.) wear out in time. Our Clarity was made in late 2017 and purchased in February of 2018 and now has just under 15,000 mostly EV miles on the car. We got the #3 maintenance reminder in December of 2023. After I changed the fluid (very easy and less than $20 for the Honda fluid and new crush washer) and reset the maintenance minder display, I now see (OBD reader) that I have six years until the next transmission fluid replacement is needed.
BTW, the brake fluid replacement is also time specified at three years. Since the Clarity has a complicated braking system with two curcuits (one normal in case the main brake by wire system fails), changing the brake fluid every three years is important to prevent corrosion (caused mainly by water absorbsion). I use a suction type bleeder to change the brake fluid so that I do not need to bleed the system or reset anything. This work is a bit more complicated as the wheels need to be off but, again, it is not hard after the wheels are off and is inexpensive as less than two quarts of Dot 4 brake fluid are needed. I will be on my second brake fluid replacement next month. Please note that the engine oil and coolant changes are also time specified (the battery and inverter coolants do not appear to have any changes needed). I have not had to change the engine coolant yet but that is more complicated as there probably are some Clarity specific bleed procedures needed and I have not seen those posted as yet.
Leop