I used WPS Hide Login which worked as described above.
When I click the button they use Javascript (I think) to open a new window and load the logged in page. There is no URL that parses information that I can see. I used Inspector Network tab to find these links:
https://sentry.io/api/1327420/envelope/?sentry_key=1111verylongnumberremoved1111&sentry_version=7&sentry_client=sentry.javascript.browser%2F7.117.0
https://mypleskdomain.com/modules/wp-toolkit/index.php/v1/installations/11/credentials
