Thunderbird 139.0.2 for Mac doesn’t highlight words as it spell checks. (bug1971121)

In the past, as Thunderbird was spell checking (triggered by pushing Send), it would highlight the words it questioned. For the last few weeks, maybe longer, it still spell checks, but the words it stops at are no longer highlighted. So I don’t know where in the body of the email the issue occurs. Without seeing the context around the potential misspelled word, I can’t tell if I should accept the suggested correction, or push Ignore. I’ve attached a screen shot of Thunderbird stopping at “interlibrary” but there is no indication at that word in the body of the email. When I tried a simpler example - one sentence with a misspelling - the misspelling was given a red underline. And occasionally, a questioned word would be highlighted. But it use to work reliably ALL the time. What can I do to bring back highlighting the questionable word? I didn’t realize how much more useful it made the spell checking.