I’ve seen this message before: “This system is locked, you’ll be redirected to the unlock dialog in a few seconds.”

This morning that message did not clear up after several minutes (including time to walk to the kitchen and get a glass of water). Finally, I had to open a text terminal, run links, visit my favourite search engine duckduckgo.com, and look up how to fix it. Thank goodness for shell tools and the ability to use them.

The answer is[0]: on the terminal,

loginctl list-sessions
loginctl unlock-session <sessionid>

Works like charm, immediately opened the session.

[0] Answer found at askubuntu. Thank you askubuntu for a useful question and answer that solved my problem in minutes. And for a page that was legible in links, the text-based browser.