Romans 11:32 according to Calvinist?

It was always God's plan, before the creation of the world, that all should sin against Him. God is completely outside of time, it makes no sense to speak of things He planned before the creation and things planned after creation. He has an eternal plan, and it has always existed since before the foundation of the world.

Of course, the "all" includes Adam and Eve and everyone else.

The reason given in the verse is so that God's grace can be displayed.

The grace is not given savingly to all, but all receive food and common blessings which they do not deserve.

The plan was God's plan, the blame for the sin is entirely ours.

The answer is in the Scripture itself according to Romans 11:30-32

³⁰ For as ye in times past have not believed God, yet have now obtained mercy through their unbelief: ³¹ Even so have these also now not believed, that through your mercy they also may obtain mercy. ³² For God hath concluded them all in unbelief, that he might have mercy upon all.

It is clearly stated that it is about the mercy of God. The key word is "mercy"; the mercy of the father to his son for the father is looking forward to the possibility of what may happen to his child. There is no such mercy you can think of if he sees his child with safer consequences.

At the very least, Romans chapters 8-11 need to be taken as a whole and, if 1-11 can be taken that way it is even better. Lone verses picked out of 9-11 are difficult to properly exegete. I am pilfering the clue given in @Sam's comment to OP in order to construct an answer:

In the large context: Rom. 9:1 -11: 35, "everyone" refers in restrict sense "the Jews and Gentiles."

The overarching thing that Paul is doing in Romans ch. 9-11 is 1) describing the special position of Israel in God's redemptive plan:

Who are Israelites; to whom pertaineth the adoption, and the glory, and the covenants, and the giving of the law, and the service of God, and the promises;  Whose are the fathers, and of whom as concerning the flesh Christ came, who is over all, God blessed for ever. Amen. - Romans 9:4-5

2. Explaining how natural descent within Israel does not automatically guarantee promise:

Not as though the word of God hath taken none effect. For they are not all Israel, which are of Israel: Neither, because they are the seed of Abraham, are they all children: but, In Isaac shall thy seed be called. That is, They which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed. - Romans 9:6-8

And 3) how those who are called, according to promise are from both Jew and Gentile:

Even us, whom he hath called, not of the Jews only, but also of the Gentiles? - Romans 9:24

Here it must be remembered that Paul has already laid out how the entire process of man's redemption, of which 'calling' is a part, begins with God's foreknowledge. Many theologians of many different stripes have attached limitation of scope or meaning here but the Scripture does no such thing. He declares the end from the beginning, we are told (Isaiah 46:10) and that, without qualification:

For whom he did foreknow, he also did predestinate to be conformed to the image of his Son, that he might be the firstborn among many brethren. Moreover whom he did predestinate, them he also called: and whom he called, them he also justified: and whom he justified, them he also glorified. - Romans 8:29-30

This whole process wherein God has offered salvation freely, by grace through faith, and has foreknown who will call on the name of the Lord in response to this offer is available to "all", meaning both Jews and Gentiles:

For there is no difference between the Jew and the Greek: for the same Lord over all is rich unto all that call upon him. For whosoever shall call upon the name of the Lord shall be saved. - Romans 10:12-13

Chapter 11 then starts with a question: Based on the disobedience of Israel outlined in chapter 10 and the offer of salvation to the Gentiles, has God utterly cast Israel aside? Of course not, says Paul, and his proof is that he, himself, is an Israelite and he has been saved:

I say then, Hath God cast away his people? God forbid. For I also am an Israelite, of the seed of Abraham, of the tribe of Benjamin. God hath not cast away his people which he foreknew. - Romans 11:1-2a

Israel (natural) has not attained the election of grace (Romans 11:5-7) because, as we have seen, election is according to God's foreknowledge and not natural descent or national affiliation. There are individual Jews who are a part of this 'remnant' (Romans 11:5) and in the Apostle's illustration they are the natural branches of the olive tree; the true, spiritual Israel; the children of Abraham by faith and heirs of the promise. Into this 'olive tree' the called Gentiles are grafted in:

For if thou wert cut out of the olive tree which is wild by nature, and wert graffed contrary to nature into a good olive tree: how much more shall these, which be the natural branches, be graffed into their own olive tree? For I would not, brethren, that ye should be ignorant of this mystery, lest ye should be wise in your own conceits; that blindness in part is happened to Israel, until the fulness of the Gentiles be come in.- Romans 11:24-25

By the time we get to the verses in question it needs to be remembered that the entire context thus far has revolved around how both Jew and Gentile have been and are being called unto salvation and shown mercy:

For as ye in times past have not believed God, yet have now obtained mercy through their unbelief: Even so have these also now not believed, that through your mercy they also may obtain mercy. For God hath concluded them all in unbelief, that he might have mercy upon all. - Romans 11:30-32

The 'all' in view here is inclusive of Jews and Gentiles. All (both groups) are shut together or included within unbelief so that all (both groups) may obtain mercy.

It is a mistake to try and force 'all' in these verses to speak in any way about each individual person or eternity past and God's intentions prior to creation other than the fact that election is according to foreknowledge.