Some JSON to use with SharePoint JSON column formatting to provide a link to a custom form.

SPFx_FormLink.json

{
  "$schema": "https://developer.microsoft.com/json-schemas/sp/column-formatting.schema.json",
  "elmType": "div",
  "children": [
      {
          "elmType": "span",
          "style": {
              "padding-right": "8px"
          },
          "txtContent": "Cross charge form"
      },
      {
          "elmType": "a",
          "attributes": {
              "iconName": "FormLibrary",
              "class": "sp-field-quickActions",
              "href": "= @currentWeb + '/SitePages/Cross-charge-form.aspx?itemId=' + [$ID]"
          }
      }
  ]
}