First, let’s clear up the distinction between Zakat (Zakah) and Sadaqah. Zakah is an obligatory act and an important pillar of the Islamic faith. It is enjoined in Islam on specific things such as possession of gold, silver, crops, fruits, trade goods and livestock, i.e., camels, cattle and sheep. As Zakat is obligatory, this means that whoever dies and owes Zakah, his heirs must pay it from his wealth, and that takes precedence over the will (wasiyah) and inheritance. (Ref: https://islamqa.info/en/9449)
With regard to Sadaqah, it is not obligatory on any kind of wealth, rather it is what a person can give, without any specific limits or guidelines.