What is this wallet file I found?

I came across an old file from 2017 called "mystery wallet" on my hard drive, and it doesn't have any extension. Back then, I was messing around with a ton of different cryptocurrencies, mining setups, and basically lost money, but I'm curious to see if this file has any value before I just delete it. So, I added a .txt extension and opened it on my Mac. It's just one long string of 2,012 characters starting with: QklFMQJD5E and it keeps going... Any ideas on what this could be? I even tried renaming it to wallet.dat and importing it into Bitcoin Core, but that didn't work. And to any scammers out there, don't bother messaging me. I don't reply to DMs.

More than likely it's an encrypted Electrum wallet.  Electrum doesn't add extensions to it's wallet files by default, so I'm just throwing spitballs based on the string at the start.   Try opening it in Electrum, but make sure you download the package from the official site and verify the PGP signatures.  If Electrum asks you for a password, then you know you're on the right track...  Then you get to try to remember your 8-year-old password.  Fun times. ETA: I suppose it could also be one the Electrum forks for other coins, i.e. BCH, Litecoin, etc.

You are a freaking genius. It was an Electrum wallet and after testing a few passwords, I found the correct one and the balance was...0 BTC. Anyway, thanks a lot for helping! Let me ask you a related question. I also have a couple of old wallets for ripple, most likely with $0 balance as well, but just in case. These are files that have a long string that starts with: eyJpdiI6IktqTVJKOG and continues How would I restore these?

Such is life. I'm afraid I won't be any help with altcoins that aren't XMR.  Ripple is one of the few alts that I was suckered into buying in my "youth," but the only wallet I've ever used for it is Trezor Suite.  I'm glad I was able to help you with the bitcoin wallet, though.

The file names would be more useful than the first few characters of the contents since most wallets are specific to their wallet file or backup naming scheme. As for a possible Electrum XRP fork (most are scams BTW), it can be anything that the owner set without any file name extension, else it's "default_wallet" or "wallet_<number>". You can also ask this in the Alts board or (unaffiliated) Alts forum where Ripple users/experts may be present.