The defence is expressly prohibited from lying. Lawyers have a so called duty of candor [1] outlining this. Defendants testify under oath to make this clear to them. Defence attorneys must disclose to the court if their client lies to the court (and they can't convince their client to voluntarily disclose it instead) [2].
That doesn't mean people are expected to take defendants at their word during trial, juries are allowed to decide they think that someone was lying, but they aren't expected to lie.
The defence is expressly prohibited from lying. Lawyers have a so called duty of candor [1] outlining this. Defendants testify under oath to make this clear to them. Defence attorneys must disclose to the court if their client lies to the court (and they can't convince their client to voluntarily disclose it instead) [2].
That doesn't mean people are expected to take defendants at their word during trial, juries are allowed to decide they think that someone was lying, but they aren't expected to lie.
[1] https://definitions.uslegal.com/d/duty-of-candor/
[2] https://www.eiglarshlaw.com/when-clients-liewhat-must-you-do...