I don't share the definition of over engineering.
As engineering is the act of solving technical problems, over engineering is about putting too much engineering effort on aspects, features or products that don't have a linear payoff to the budget spent.
E.g. I worked in a company that was obsessed with unit test coverage metrics and the effort of maintaining the test suite was considerably biting in the ability to move the product. The ratio was 25% of product and 75% of unit tests.
And the payoff was small if not even negative, impacted morale, productivity and actively pushed back against refactors, because any large refactor was met with a disproportionate effort in unit test rewriting. Let alone the fact that as you were mocking external dependencies, and the mocks costed engineering effort and internals digging, it also suppressed work to keep it up to date.
I never got to convince the org to shift focus on E2E testing, which answered the real questions: does the product make money and works as expected. Uni test had to be used when writing a parser, not to validate some react scroll component as browser apis and the triggers mimicking costed days of work.
In fact we often had gigantic all green test suites for broken products.
That's to me over engineering an aspect of the engineering cycle.
This is a good way of putting it. People who advocate for over-engineering don't consider cost-benefit vs not doing it. This is where FMEA analysis comes in when developing products, you assign values for severity, occurrence, and detection to determine which potential issues need extra effort implemented, but just as important is identifying the potential issues that aren't worth putting effort into to prevent over-engineering.
I've recently had to deal with a problem where the parent company has dictated 100% production testing for a spec that we meet for the spec sheet but customers practically don't ever need. But since the parent company test their products this way they say we have to. I've been very vocally against this because it has delayed us shipping products that are otherwise ready, prevented starting new products, and added a lot of production cost when our RMA rate without the test is something on the order of 0.01% and most of those are due to installation errors, not true failures.