Wufoo.com -> Demo -> Form Settings -> Pasting the key in the description caused the preview to show the key.
This was sort of finicky to do, I'm not sure how reproducible it is? I also had the BTC key shoved in a bunch of other fields, some of which became partially visible.
Pasted the private key into the email address field on the Wufoo signup page, and the validator helpfully told me my "email" was invalid, with the whole key included.
Launch Electrum, create a new wallet, "Import Bitcoin addresses or private keys", paste in the recovered key.
If you just paste the raw key, Electrum uses a legacy format, and none of the transactions show up for that private key. Adding the "p2wpkh:" prefix to the key makes the transactions show up, but I realized that well after someone else claimed it.
I don't know if this is an Electrum thing, if this is considered general knowledge now for those who regularly use BTC, or if it's a quirk of how BTC has evolved.
fwiw I was able to get a private key out of the system, but there's no BTC/transactions associated with it. Dunno if that's an error on my part (although the key has a valid checksum) or the wrong key got uploaded.
This was sort of finicky to do, I'm not sure how reproducible it is? I also had the BTC key shoved in a bunch of other fields, some of which became partially visible.