2018 Mitsubishi Outlander — coolant is old by age but mileage is low — anyone dealt with this recently?

Start with the test that can prove you wrong. Loaded-suspension checks on the 2018 Mitsubishi Outlander catch play that a wheels-hanging inspection misses. That's the branch I'd chase this week. Verbal 'we'll take care of it' is not a plan. I've seen both outcomes, which is why I'd test instead of assume. Doing the boring step first on purpose.