"Lest" isn't a very commonly used word, so there's that. However, some of us like using it. I'm not sure I understand your question since you say you know what it means but you are not looking for example sentences. So what are you after exactly? I'm happy to help if I understand your question better.

It means “because of the unwanted possibility that”. This requires subjunctive mood, as does “lest”

It is a fairly "literary" word, used more in written English than spoken English, and more often in older writing. I would define it as "so that you don't" or "in case." It is often part of the colocation "lest we forget," which MIGHT be a reference to a famous poem by Rudyard Kipling, "Recessional." I like to use Google News searches to find usage examples, because newspapers and journalism tend to be good contemporary English. I find plenty of examples of "lest." Here are a few of them: Be on your guard, lest you find yourself on the receiving end of an April Fool’s Day prank. (Describing a role-playing game) When the music ends, players must find a seat at a nearby region lest they fall under the influence of the various sea gods patrolling the floor. Lest one suppose that five percent inflation is no big deal, look at the numbers leading up to August 15, 1971, when President Nixon slammed shut the gold window and ushered in the age of stagflation.

Ways to say a similar sentence: To avoid the possibility that you think I exaggerate, here are the ABCs ... To prevent your thinking that I exaggerate, here are the ABCs ... To counter your possibly thinking that I exaggerate, here are the ... It is indeed an unusual way to say such things, but useful at times.

in the sentence you used, lest you you think i'm exaggerating, it basically means to prevent you from thinking i'm exaggerating, so the meaning you have is correct, you use that when you want to say that you would like to prevent something from happening so it's a nice way of saying i'm preventing you from thinking i'm exaggerating, however it is a very formal word mostly used in business environments, not a very conversational word so i would not worry about that too much, you basically use it instead of saying please don't think i'm exaggerating when i say the following