The problem with displaying google picker in apps script when placing the script in a iframe of another web site. When you call the picker, a white square is displayed.
Not in the frame of another web site, the picker works fine.
HtmlService google apps script
function doGet() {
return HtmlService.createTemplateFromFile('form.html')
.evaluate()
.setXFrameOptionsMode(HtmlService.XFrameOptionsMode.ALLOWALL);}
https://stackguides.com/questions/40842627/embedding-google-apps-script-in-an-iframe#answer-40843413
The picker is based on this documentation -
https://developers.google.com/apps-script/guides/dialogs#file-open_dialogs
I decided to try a demo premium script File Upload Form.
Will insert the script into the frame, but the result was similar - an empty white square.
https://script.google.com/macros/s/AKfycbxlX3r_dt_ZLZC9TqloaqtdextROJoIH9mUDu3MWOiXtI6ADhqb/execExample
Whether it is possible to solve this problem.