Bearded dragons definitely are not able to drop or regrow tails. Once they have tail damage or lose
portions of their tails, it is permanent. Iguanas don't drop their tails but if they lose small portions of
it "it can grow back but in limited portions" meaning it will never be the length it was previously.
Geckos do have the ability to drop & regrow tails. It can be stressful for them to go through this & to
have to regrow a tail.
A lot of lizards can drop their tails and regrow them but the new growth looks different and obvious. As mentioned, beardies + iguanas do not. Most types of anoles, fence lizards, geckos, skinks and many others do .