Laptop is asking for a BitLocker recovery key I've never heard of

If the key isn't in your Microsoft account, think about which account was used the very first time the laptop was set up. It's often an old hotmail address or a family member's account, and the key is in that one. Also check any file or printout from when you got it. If it's truly nowhere, the data can't be recovered without it, and the only way forward is reinstalling Windows.

Don't panic and don't reset it yet. A lot of laptops turn on device encryption quietly the first time you sign in with a Microsoft account, so you never set it up but the key still got saved. 1. On your phone or another computer, sign in to the same Microsoft account you use on the laptop and look under your devices for the BitLocker recovery keys section. 2. Match the Key ID shown on the blue screen (the first 8 characters are enough) to the one in the list, then type the 48-digit key. If it's a work or school laptop the key is held by their IT, not you, so ask them. Very often what triggers this is a BIOS or firmware update, or changing something in the BIOS, so once you're back in it shouldn't keep asking.