I wouldn’t be surprised if Chinese had no irregularities in the tense system – it’s a very isolating language. But here’s one irregularity: the negation of 有 is 没有 (“to not have/possess”), but the simple negation of every other verb is 不 + verb. You can negate other verbs with 没, but then it’s implied to be 没有 + verb, which makes the verb into something like a present participle. E.g., 没吃 = “to have not eaten”.
I wouldn’t be surprised if Chinese had no irregularities in the tense system – it’s a very isolating language. But here’s one irregularity: the negation of 有 is 没有 (“to not have/possess”), but the simple negation of every other verb is 不 + verb. You can negate other verbs with 没, but then it’s implied to be 没有 + verb, which makes the verb into something like a present participle. E.g., 没吃 = “to have not eaten”.