You are using discrete x-axis (bands) rather than continuous. I would do something like this.
[![enter image description here][1]][1]
{
"$schema": "https://vega.github.io/schema/vega-lite/v5.json",
"width": 800,
"height": 200,
"data": {
"values": [
{
"pre_120": 10,
"pre_90": 15,
"pre_60": 30,
"post_60": 100,
"post_90": 150,
"post_120": 200,
"type": "Mango"
},
{
"pre_120": 50,
"pre_90": 30,
"pre_60": 45,
"post_60": 90,
"post_90": 140,
"post_120": 190,
"type": "Apple"
}
]
},
"transform": [
{"fold": ["pre_120", "pre_90", "pre_60", "post_60", "post_90", "post_120"]}
],
"layer": [
{
"mark": "line",
"encoding": {
"x": {
"field": "key",
"bandPosition": 0,
"axis":{ "bandPosition":0, "labelOffset":-55},
"sort": [
"pre_120",
"pre_90",
"pre_60",
"0",
"post_60",
"post_90",
"post_120"
],
"scale": {
"domain": [
"pre_120",
"pre_90",
"pre_60",
"0",
"post_60",
"post_90",
"post_120"
]
}
},
"y": {"field": "value", "type": "quantitative"},
"color": {"field": "type", "type": "nominal"}
}
},
{
"mark": {
"type": "rule",
"color": "maroon",
"size": 3,
"strokeDash": [6, 4]
},
"encoding": {"x": {"datum": "0", "bandPosition": 0}}
}
]
}
[1]: https://i.stack.imgur.com/Vu8mP.png
[![enter image description here][1]][1]
{
"$schema": "https://vega.github.io/schema/vega-lite/v5.json",
"width": 800,
"height": 200,
"data": {
"values": [
{
"pre_120": 0,
"pre_90": 0,
"pre_60": 0,
"post_60": 100,
"post_90": 150,
"post_120": 200,
"type": "Mango"
},
{
"pre_120": 0,
"pre_90": 0,
"pre_60": 0,
"post_60": 90,
"post_90": 140,
"post_120": 190,
"type": "Apple"
}
]
},
"transform": [
{"fold": ["pre_120", "pre_90", "pre_60", "post_60", "post_90", "post_120"]}
],
"layer": [
{
"mark": "line",
"encoding": {
"x": {
"field": "key",
"sort": [
"pre_120",
"pre_90",
"pre_60",
"0",
"post_60",
"post_90",
"post_120"
],
"scale": {
"domain": [
"pre_120",
"pre_90",
"pre_60",
"0",
"post_60",
"post_90",
"post_120"
]
}
},
"y": {"field": "value", "type": "quantitative"},
"color": {"field": "type", "type": "nominal"}
}
},
{
"mark": {
"type": "rule",
"color": "maroon",
"size": 3,
"strokeDash": [6, 4]
},
"encoding": {"x": {"datum": "0"}}
}
]
}
[1]: https://i.stack.imgur.com/xKCyf.png