Paul did not have a vision. Paul says that Jesus appeared "last of all" to him: "Last of all" entails that Jesus stopped appearing to people after Paul's "appearance" as far as he was concerned, yet Paul himself admits that "visions and revelations" of Jesus occurred after the end of the chain in 2 Cor 12:1-2. 2 Cor 12:1-2 describes a later experience Paul had:
"I must go on boasting. Though there is nothing to be gained by it, I will go on to visions and revelations of the Lord. I know a person in Christ who fourteen years ago was caught up to the third heaven—whether in the body or out of the body I do not know; God knows." (2 Cor 12:1-2)
Yet this later vision of Jesus came after Paul closed the canon on Jesus appearances. So Paul is implicitly excluding subjective visionary experiences as his resurrection appearance. See James P. Ware (2019, p. 281). Karl Olav Sandnes, Jan-Olav Henriksen agree with Ware:
By claiming the position as the last among Easter witnesses, Paul conveys that the appearances of the risen Jesus are of a special kind. In Paul’s charismatic world-view, where revelations and visions were normal phenomena (Gal 2:2; 2 Cor 12:1; see below), the claim to be the final witness implies that something more than visions in general is at play here.
(Karl Olav Sandnes, Jan-Olav Henriksen, Resurrection: Texts and Interpretation, Experience and Theology, 2020, p. 104)
Paul says that he received a "revelation of Jesus Christ" that was not of human origin in Gal 1:11-12:
Galatians goes on to explain how Jesus appeared in him (Gal 1:16).
The translation in Galatians is likely "to me," not "in me." Charles L. Quarles writes (2019):
Although the NRSV and the ESV (I will argue correctly) translate the clause “[God ] was pleased to re veal his son to me” ( italics mine), both refer to marginal notes that state “Gk . in me” and “Greek in” respectively. The notes give the impression that the Greek preposition is the equivalent of the English preposition “in” and would seem to suggest that the translators adopted an alternative rendering for theological purposes rather than linguistic reasons.
[...]
The use of the en phrase with verbal constructions related to revelation in the LXX, NT, and particularly elsewhere in Paul restricts the interpretive options considerably. The preposition en is never used elsewhere in the LXX or the New Testament with these constructions to indicate a mere internal, subjective experience.
https://hbu.edu/news-and-events/2016/07/01/paul-witness-r-esurrection-jesus/
The icing on the cake is when Acts has Paul says he has a visiion (optasia) explicitly:
“After that, King Agrippa, I was not disobedient to the heavenly vision [optasia]." (Acts 26:19)
To think that Luke’s use of optasia in Acts 26:19 only refers to a subjective vision is simply mistaken. The word can refer to something seen only subjectively, such as in a dream. But it can also be used of objective sight of tangible objects. For instance, Sirach chapter 43 refers to the optasia of the sun (en optasia helios, “the sun when it appears”). The sun is hardly a subjective vision or dream. More importantly though, Acts describes external and physical elements and consequences (such as Paul's physically damaged eyes) for Jesus's appearance, which seems to rule out the idea that the author of Luke-Acts thought of Paul's experience as visionary as we would understand it today. Rather, the author of Acts seems to employ optasia to denote a supernatural appearance of Jesus. Luke likewise calls the encounter the women had with the two men (meant to be angels) at the empty tomb in Luke 24:1-12 a "vision" in Luke 24:23, yet this clearly was not a subjective inward experience as we would understand a vision today.
Paul doesn't see anything but light, and the accounts contradict. Him falling to the ground is consistent with Paul having a seizure.
Heavenly beings were also understood to have spewed light when phyiscally present (Ezek. 10; Dan. 7.9; 10.5-6; Lk. 2.9; Acts 1.10; 2 Cor. 11.14; Rev. 4.4; 10.1; 1 En. 62.15-16; 2 En. 22.8). The light just indicates Jesus' body of glory being present ... physically. Paul "characterizes the body of resurrection as that of glory (1 Cor 15:43) and explicitly calls the body of the Lord Jesus Christ 'the body of glory' (Phil 3:21). In the bible δόξα normally means 'heavenly and divine radiance' or the 'divine mode of being' made visible as radiance. So the risen Christ must have appeared accompanied by the radiance of light which was perceived by him as the divine glory."(Seyoon Kim, The Origin of Paul’s Gospel, [Tübingen: Mohr Siebeck, 1981], p. 8)
Furthermore, the Acts accounts support viewing the experience as objective. The bystanders saw the light from heaven (though they did not see Jesus) and fell to the g round along with Paul. They also heard the voice (though for reasons not explicitly identified the y did not understand the words uttered by the voice). These factors indicate that the appearance of Jesus to Paul was not a mere vision experienced only in his imagination.
The appearances of Jesus in the Gospels also seem in direct contradiction with Paul's spiritual resurrection:
What I am saying, brothers and sisters, is this: flesh and blood cannot inherit the kingdom of God, nor does the perishable inherit the imperishable. (1 Cor 15:50)
Regarding the phrase "flesh and blood" denotes human fragility and not composition. John Granger Cook writes:
"“flesh and blood” – in particular its use as a rabbinic expression which simply refers to human nature in its fragility and not simply to “physical flesh.” An early rabbinic example is from the Mekhilta of Rabbi Ishmael where Exod 12:12 “I am the Lord” is explained as “What flesh and blood cannot say.” Another occurrence is a discussion of Exod 15:1 “I will sing unto the Lord for he is really exalted,” which is explained by an example that begins “when a king of flesh and blood enters a province …"
(John Granger Cook, Empty Tomb, Resurrection, Apotheosis, Mohr Siebeck, 2018, p. 585)
Paul also calls our post resurrection body a "spiritual body" (1 Cor 15:44-46)
What Paul has in mind when he says "it is raised a spiritual body" is a physical body that is empowered by the Spirit of God. What he does not have in mind is some ethereal body. In 1 Cor 2:14-15, Paul makes a similar distinction between psychikos and pneumatikos, and what this means is being able to understand the things of the spirit. 1 Cor 2:14-15 says:
Those who are unspiritual do not receive the gifts of God’s Spirit, for they are foolishness to them, and they are unable to understand them because they are spiritually discerned. Those who are spiritual discern all things, and they are themselves subject to no one else’s scrutiny.
It makes no sense imaging Paul speaking about person composed of soul verse those composed of pneuma. Further examples of this phenomenon can be seen through the First Epistle to the Corinthians. The adjective pneumatikos is used to reference persons or things empowered by the Spirit of God, such as: palpable manna and water (10:3–4), a tangible rock (10:4), and flesh and blood human beings (2:15; 3:1; 14:37). Used with soma in 15:44, the adjective pneumatikos indicates that the risen body will be a physical body given life and empowered by God’s Spirit.