Thanks for reaching out! A blank screen could mean that there is a fatal error going on. It can be caused by an outdated plugin or any other thing. Please go to your plugins section first and make sure that all the plugins are up to date. Second, go to Tools > Site Health and make sure that there are no Performance issues going on.
If the above suggestions still do not work and the blank white screen is still going on, kindly enable the debug mode. You can do this by opening wp-config.php and adding
/* That's all, stop editing! Happy blogging. */
When you revisit the widget page or the blank white screen, you should have some error output describing the issue in more detail.
Kindly let us know how it goes.