In General, Christians believed there was a stark difference between appearances of Jesus and visions of him.
Paul took it for granted that he and his audience all knew that appearances of Jesus were special, and stopped long ago (ending with Paul).
A full page will analyze at least these 6 positive arguments:
This is relevant because, long after Paul had received this initiating conversion-appearance from Jesus, he and other Christians nevertheless continued to experience literal “visions” (i.e. non-physical visualizations etc. of Jesus). So appearances and visions are quite distinct in the mind of Paul and early Christians.
Paul writes in 1 Cor 9:1 — “Am I not an apostle? Have I not seen [ἑὠρακα ] Jesus our Lord?” which—in the original Greek—implies its consequence persists.
This is relevant because it implies his conversion experience was unique and not repeated.1
Paul never includes his Damascus road experience when discussing them. This is relevant because it seems like there was plenty of opportunity for him to (e.g. 2 Cor 12:24)
While the church rejected that later people received an appearance from Jesus, the apostles (Peter etc.) acknowledged that Paul did receive one.1 This is relevant because the church did not acknowledge that all Christians received an appearance, and if the Jerusalem church differentiated these then likely Paul did as well.