Does everyone already understand that hilasterion, (ιλαστηριον, rendered "propitiation"), is not a verb but a noun? It is the word used for the mercy seat upon the ark of the covenant. Perhaps the Young's Literal Bible Translation can help to clarify this whole matter and passage. The righteousness of Elohim through the faithfulness of Messiah is to/unto/toward ALL, (because it is a genuine offer unto ALL), and-moreover [it is] UPON all those believing, (because it is not yet UPON those not yet believing). However that portion of the passage is not the same in the W/H and GNT morph texts, (the KJV and the YLT read from the Textus Receptus and Byzantine text family), but since the KJV is the most popular therefore I say that perhaps the YLT, (which reads from the same text as the KJV), may shed some light:
Romans 3:21-26 YLT (Young's Literal Bible Translation)
21 And now apart from law hath the righteousness of God been manifested, testified to by the law and the prophets,
22 and the righteousness of God is through the faith of Jesus Christ to all, and upon all those believing, --for there is no difference,
23 for all did sin, and are come short of the glory of God--
24 being declared righteous freely by His grace through the redemption that is in Christ Jesus,
25 whom God did set forth a mercy seat, through the faith in his blood, for the shewing forth of His righteousness, because of the passing over of the bygone sins in the forbearance of God--
26 for the shewing forth of His righteousness in the present time, for His being righteous, and declaring him righteous who is of the faith of Jesus.
"TO-UNTO-TOWARD ALL", (a genuine offer to-unto all), and-moreover, "UPON" all those believing.
The Reform-Calvinist view which was previously posted and quoted is refuted in this passage, (if reading from the T/R and Byzantine text family as above herein), for it is clearly indeed a genuine offer "to all", but that does not mean that the genuine offer is bestowed "upon all", for Paul says it is "upon all those believing".