It's been like ten years since I've used Plesk, however, I know most panels offer some type of limited-capabilities demo account.
Check out this page, may or may not be what you're looking for: https://support.plesk.com/hc/en-us/articles/115001407434-How-to-access-Plesk-demo-servers-
You can also run a search either on Google or Plesk.com for "demo mode" or "demo account" and it should turn something up.