Google is testing out large titles that are completely bolded for Google Ads results. Here is a screenshot from Andrew Rodgers on twitter:
— //Andrew Rodgers ☘ (@AndyNRodgers) July 9, 2020
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Google might not be bolding the title because it gets along with anything in the search query box but to test a new look. It has also been said that these are not specific to Ads. Just the very top results so it also applies to organic if there is not an ad there.