ClipQuery is a web app (clipquery.com) that lets you ask questions about YouTube videos: it answers from what is actually said, shows the exact moment, and can compare what several videos say in one table. The Basic plan is free forever with no card.
Without any tool: open each video's transcript (under the video description, or the three dots under the video, then Show transcript), search it for the same keywords, and note the answers in a table by hand. It is reliable, but it takes about as long as watching.
A real example: three videos about sleep (4:35, 5:45 and 8:37, 18 minutes 57 seconds in total). The question was "Compare what each video says happens to your brain and body during sleep." The table came back in about 13 seconds. It showed that all three talk about the brain and the body, but one of them never mentions memory at all.
How many videos you can compare at once depends on the plan: Basic compares 2, Pro 5 and Beast up to 10. The answer comes from the videos' transcripts, so it can be imperfect; the table lets you check each point. You sign in with Google; ClipQuery keeps only your email address.
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Up to 10 on the Beast plan, 5 on Pro and 2 on the free Basic plan.
The table says "not mentioned" for that video, so you can see at once which video skips the point.
Yes. It works with videos in any language that have captions or can be transcribed.
The Basic plan is free forever with no card. Pro is $9 a month and Beast is $45 a month, each billed once for the period with no automatic renewal.