Microsoft is testing bolding the title links in the Bing search results for both the organic and paid listings. I am not sure if this was a bug or a test, but I suspect it was a test.
This was spotted by Sachin Patel, who posted a couple of screenshots on X - here is one of them:
I do not like this, but what do I know?
Forum discussion at X.
Note: This was pre-written and scheduled to be posted today, I am currently offline for Rosh Hashanah.