They are very close in meaning, but not exactly the same. “I didn’t give it much thought” means you did not spend time considering something in a serious or careful way. “I didn’t think much about it” means you did not think about it often or for a long time. In many situations, they can be used the same way, but the first sounds slightly more formal and focused on careful consideration, while the second sounds slightly more casual and about general thinking.

British English accent overall, and very natural. You didn't write the second pair, which appears to be pull/pole. Your accent shows there.

I didn’t give it much thought = you did not spend much time thinking about or considering something. I didn’t think much about it = you don’t have a strong opinion about something or you don’t consider it important or good quality. Another way of saying ‘I didn’t give it much thought’ is -‘ I didn’t think about it much’ I just repositioned the subject of the sentence.