Rom 8:29 For whom He foreknew, He also predestined to be conformed to the image of His Son, that He might be the firstborn among many brethren.

Romans 8:29 is often used as a prooftext of God knowing all future events from all eternity:

This knowledge is not a posteriori, obtained by observation, but a priori, present from eternity (1 Cor. 2: 7; Rom. 8: 29; Eph. 1: 4– 5; 2 Tim. 1: 9).

Bavinck, Herman. Reformed Dogmatics : Volume 2: God and Creation (p. 166). Baker Publishing Group. Kindle Edition.

A few items of note about Romans 8:29:

1. This does not indicate when God “foreknew” individuals, not less does this indicate this knowledge was present from eternity.
2. This does not indicate how God “foreknew” individuals, not less does this indicate this knowledge is “a priori”.
3. This does not indicate in what way God “foreknew” individuals. The word is used for relationships, not a conceptual knowledge, but a relational knowledge formed by interaction. Paul uses the word for people who foreknew him:

Act 26:4 “My manner of life from my youth, which was spent from the beginning among my own nation at Jerusalem, all the Jews know.
Act 26:5 They knew me from the first, if they were willing to testify, that according to the strictest sect of our religion I lived a Pharisee.

Paul is not talking about knowledge that pre-exists the object of the knowledge. Instead he is using the word to indicate that these people, in the past, had familiarity with Paul.

A few points about Paul use of “foreknowledge”:

1. The knowledge is obtained as events happen in the past.
2. The knowledge is obtained through interaction, or observation.
3. The knowledge is not eternal, but generated knowledge.

Romans 8, being used as a prooftext for knowledge which “a priori, present from eternity” is a stretch.