Pressing and holding on a key no longer brings up the character accents menu

Has anyone else had this problem with Sequoia 15.1.1?

Suddenly the ability to type a letter with special linguistic accents etc is no longer available, thus pressing and holding a key merely makes that character repeat endlessly.

I didn't find a fix as such, but restarting the Mac fixed it. Apparently this has been an ongoing issue across various operating system versions - and others have reported that restarting is just a temporary fix.