Is it permissible to apply mascara that volumizes, lengthens, and thickens the eyelashes, knowing that it may serve as an alternative to kohl, especially in the context of the prohibition of artificial eyelash extensions?

There is no harm in using mascara, as it is a permissible adornment like kohl, provided it is not displayed in front of non-mahram men. It does not matter if it makes the eyelashes appear longer or thicker. It is important to note that some types of mascara may prevent water from reaching the skin, which affects the validity of ablution.