Myth or Truth? : Heavier dumbells make a woman muscular, lighter weights with more repetition make her leaner

Myth or Truth? : Heavier dumbells make a woman muscular, lighter weights with more repetition make her leaner I'm a woman, 167cm height and probably 70kg in weight. I've had 3 pregnancies (one of them twins). I naturally have strong arms (runs in the family, short and strong). In the pandemic I went down to 55kg through diet and bodyweight (no equipment), just at home (I used Mark Lauren's training programs). So I went today to buy dumbbells, I was thinking of 4 kg, I saw some excersices on YT and they (woman trainer) use 4kg too. The guy was adamant I should go for lighter "cause most women ask him up to 3 so they won't get too buffy and that with more repetitions it should work better". He also said to check with a gym trainer first. I said I've been hearing more and more women saying that's a myth. That it's decided by your genetics the maximum you can become buffy and that to look buffier you'll need to be a pro bodybuilder that has a whole diet on that and possibly meds, supplements etc. I finally got irritated and decided not to buy the lighter ones. So, what is it then? Can women use heavy dumbbells? I'm trying to replace fat with muscle. I was planning to have cardio (spinner bike) and dumbbells/elastic band loops.