Ideas shared with you
When someone invites you, you'll get an email with Join the idea. If your confirmed email matches, the invite also waits on Home, with Join and No thanks.
Ideas shared with you are under Shared › With you, with the owner's name and whether you can edit or view.
To leave an idea, open it, tap the ⋯ menu, and choose Leave this idea. It's gone from your list, and the owner can invite you again later.
If an invite says it has expired or was turned off, ask the owner for a new one.