I need like a list of every sexuality, because I have no idea what 99% of people are talking about.
You may want to check out the book & YouTube series The ABCs of LGBT+ by Ash Hardell/Ashley Mardell (her book is published under her old name). It’s a pretty good overview.
Although honestly I don’t think anyone knows or can know every single sexuality, since new terms are being coined all the time. Generally, if someone comes out as something you’ve never heard of, it’s completely fine to say “I’ve never heard of [insert identity], can you explain what it means to you?”