Can sortorder of a sitecore item be change or set during a Create or Edit through the Sitecore Restfull API. It seems you can only read standard fields?
Sitecore Version 9.3
Instead of using the string approach written in the sitecore documentation https://doc.sitecore.com/developers/93/sitecore-experience-manager/en/the-restful-api-for-the-itemservice.html when sending the data for the item creation, for example:
xhr.send("{\n \"ItemName\": \"Home\", \n \"TemplateID\": \"76036f5e-cbce-46d1-af0a-4143f9b557aa\",
\n \"Title\": \"Sitecore\" \n}");
you can use this approach instead to set the sortorder during Create Item:
var obj = {};
obj['ItemName'] = "Home";
obj['TemplateID'] = "76036f5e-cbce-46d1-af0a-4143f9b557aa";
obj['__Sortorder'] = "you custom sort order value";
xhr.send(JSON.stringify(obj, null, 4));
Same approach can be used when editing an item, you can set other standard fields as long as you set the correct field names, for example obj['__Final Renderings']