In the platonic ideal of technical debut it should have zero direct impact on users. Indirect impacts are a slowdown in the release of new features, and or bug fixes etc.

Impact is impact. Slower roll-out of future releases is already way more specific than a vague arbitrary term "technical debt", right?

I challenge you to come up with a situation where technical debt is a better way to describe activities than indirect impact as you are doing here.

How about someone saying “The X has _.”

For one it’s more specific. Saying the existing code has indirect impact doesn’t even define if it’s a good or bad impact. If you want to say, the existing code has long description that just means technical debt then sure they mean the same thing but the term technical debt is more concise.

You can still add all the low level details, but redundancy in communication still aids clarity.