What is the ruling on cleansing the navel if it contains skin tags resembling moles, and are these tags considered dirt that prevents purification?

It appears that these pimples are either part of the body or dirt resulting from congealed sweat, and your ritual purification (ghusl) is valid in both cases. You are not required to remove this dirt if it originates from the body. Al-Isnawi mentioned that the validity of ablution (wudu) and ritual purification (ghusl) is not affected by the presence of something adhering to the body that prevents water from reaching it, if it is dirt originating from the body, such as congealed sweat, unlike dirt that originates from dust.