The newer low flow fixtures and appliances sometimes don't seem to demand enough water volume to trigger or keep the water heater going. You might want to see if adding a recirculating loop would help.

"High-end" dishwashers typically have assured on-board water heating so it's probably less of a concern than the washing machine, depending on whether or not the washer also has heating for all cycles and temperature choices. Running the kitchen sink faucet hot to clear the standing cold water before starting the dishwasher should help it but but perhaps not as much the washing machine depending how its supply line is routed.

When designing plumbing - particularly with a tankless heater - the water heater needs to be close to the point of use. A water heater in the garage, and then a master bath 40 feet away at the other end of the house is in for a long wait.

Not using oversized pipes for the hot water is also helpful - as is insulating them.

When I ran my dishwasher line, I used 3/8" PEX to the manifold. Insulation helps keep it warm between refills on the same cycle.

If you are on a branch setup, yes, the Dishwasher is often plumbed to the kitchen faucet line. You can run that until it's warm - you can rinse dishes or clean the sink if you don't want to waste water.

A recirculating pump can reduce wait times, but can also increase energy use because of the heat loss in the pipes.