Is it permissible to make up for many missed prayers whose exact number is unknown, but can be estimated (e.g., one hundred prayers) with certain numbers preferred for each prayer (e.g., 20 Fajr and 50 Dhuhr)?

If you have missed prayers (fawait) and do not know what they are, you must make up the five daily prayers to clear your conscience. If you are certain that specific prayers were invalid and you have a strong presumption as to their number, you must make up those prayers. Strong presumption in this context is treated as certainty. As for prayers whose specific identity you are ignorant of, you must make up all five daily prayers for each one of them. It is obligatory to make up the missed prayers in their proper order, and if you do not remember their order, make them up as you wish. If you doubt the invalidity of prayers but are not certain of their invalidity, you are not required to repeat them, as the original presumption is their validity. It is advisable to disregard intrusive doubts (waswas), as the most effective cure for them is to ignore them and pay no attention to them.