Is my previous ghusl from janabah invalid and must it be repeated, and am I obliged to repeat the missed prayers, due to the presence of dirt in the navel that was not removed for fear that it might be part of the body?

The inside of the navel is treated like the outer surface, so it must be washed during the ritual bath (ghusl (definition)) from major impurity (janabah (definition)). Whoever neglects washing it, their ghusl is invalid. Water must reach the folds of the body, the inside of the navel, the inner parts of the ears, the armpits, and other areas that are treated like the outer surface.

If dirt prevents water from reaching the skin, and this dirt originated from outside the body, then the ghusl is invalid. However, if the dirt originated from the body, such as dried sweat, then the ghusl is valid because it is not considered a barrier.

If the ghusl was invalid, then according to the majority of scholars, you are obligated to repeat the prayers performed during that period. Some scholars, however, do not deem redoing them necessary in this situation. According to the majority view, you are obligated to make up the prayers as much as you are able, provided it does not harm your body or livelihood.