according to catholic doctrine, the patriarchs died in the friendship of God, but, since they lived (and died) before Christ, they could not enter into the kindgom of heaven.
so, the idea is that Christ retrieved them from purgatory. that’s what he was doing for those three missing days before he was resurrected.
That Christ retrieved the OT saints from purgatory may be tradition, however we are told the following from Christ:
Luke 16:
19 “There was a certain rich man who was clothed in purple and fine linen and fared sumptuously every day. 20 But there was a certain beggar named Lazarus, full of sores, who was laid at his gate, 21 desiring to be fed with the crumbs which fell from the rich man’s table. Moreover the dogs came and licked his sores. 22 So it was that the beggar died, and was carried by the angels to Abraham’s bosom. The rich man also died and was buried. 23 And being in torments in Hades, he lifted up his eyes and saw Abraham afar off, and Lazarus in his bosom.
24 “Then he cried and said, ‘Father Abraham, have mercy on me, and send Lazarus that he may dip the tip of his finger in water and cool my tongue; for I am tormented in this flame.’ 25 But Abraham said, ‘Son, remember that in your lifetime you received your good things, and likewise Lazarus evil things; but now he is comforted and you are tormented. 26 And besides all this, between us and you there is a great gulf fixed, so that those who want to pass from here to you cannot, nor can those from there pass to us.’
From Christ's own description in this parable there were two places. One of comfort at the bosom of Abraham and one of torment. There was a gulf between them each could not pass from one to the other.
Some more info in the following:
Ephesians 4:
7 But to each one of us grace was given according to the measure of Christ’s gift. 8 Therefore He says:
“When He ascended on high, He led captivity captive, And gave gifts to men.”
9 (Now this, “He ascended”—what does it mean but that He also first descended into the lower parts of the earth? 10 He who descended is also the One who ascended far above all the heavens, that He might fill all things.)
Lastly? What did Jesus tell the repentant sinner hanging on the cross next to Him? That he would be in Paradise with Him that day.