There are two views on this. According to one view, you cannot do that as you need to fast each one separately. There is another view held by some scholars; one may make a double intention and thus will be rewarded for both.

Having said this, let me point out: it is better for you to make up for the fasts of Ramadan you have missed first and then choose to fast some other days to make up for the recommended ones-if you can. If you are unable to do this, you may still gain blessings through other types of good deeds you can afford to-visiting the sick, giving charities, extra prayers, practicing constancy in dhikr, reading the Qur’an, etc.

Mind you, there is no dearth of virtuous deeds. They are all around us, if only we are willing to open our eyes and seize the opportunities.

Allah Almighty knows best.

https://islamstory.com/en/artical/1827