To clarify, what I did when I got into bitcoin was download the Bitcoin core program, was assigned a wallet, and started using Bitcoin faucets to obtain coins to the address the program gave me. I believe at some point I had that wallet in Multibit, which is why I have multibit.wallet files on some old drives of mine. I also have a multibit.key and wallet.dat files. I NEVER set a password for any of these files, but for some reason, every time I open the .wallet file in one of these newer programs, it asks for a password. (I've even tried making a new wallet and not setting a password, and these new programs still ask for a password.)
You could not have had the "same" wallet in Bitcoin Core and MultiBit... they are two different programs, with completely different wallet file formats. You cannot use a Bitcoin Core wallet.dat in MultiBit... and you cannot use a ".wallet" file from MultiBit in Bitcoin Core.
You might have been able to export/import the keys between the different wallet applications, but you could not have simply opened the wallet file. Likewise, you can't simply open these files in "these new programs"... all the wallet applications have their own wallet formats and they're generally not compatible with one another.
It's also entirely possible that you had 2 completely different sets of private keys/addresses in the two programs... one set in Bitcoin Core and one set in MultiBit.
If you have a multibit.key file, that is generally a private key "export" file... If it was not password protected, then you should be able to open it in a text editor (I'd recommend Notepad++
https://notepad-plus-plus.org/) and view the private keys... It should look something like this:
# KEEP YOUR PRIVATE KEYS SAFE !
# Anyone who can read this file can spend your bitcoin.
#
# Format:
# [[]]
#
# The Base58 encoded private keys are the same format as
# produced by the Satoshi client/ sipa dumpprivkey utility.
#
# Key createdAt is in UTC format as specified by ISO 8601
# e.g: 2011-12-31T16:42:00Z . The century, 'T' and 'Z' are mandatory
#
L4eBXv6aaE75ysQNMGfdWVWsoSikz8M1FcxeZa3Jx3P1Gyxy2MuX 2019-04-21T13:35:56Z
L52mJcSfHEA8qvYM2hGBR834zL65QD7Q6YYHviDUXSi989c7wBqJ 2019-04-21T13:35:56Z
# End of private keys
However, if it is just "gibberish" that starts with "U2F" and looks something like this:
U2FsdGVkX18LSYm98B5HRgLWHgx35xMcsSpjjtdC9XG6iEYh9OC+vfyQA1fNmjEKs64cm/bntH7g
/AMeb5NNSEe9hzYAgp/DRvOR+GX9E95pGcl4Gb2AHGMyUfAww7uV
Then it is encrypted and you did set a password when the export file was created...
In any case, you should be able to install Multibit Classic 0.5.19 and simply open the .wallet file... Even if it has a password set, it won't ask for the password until you attempt to either send coins or export the private keys. You should still be able to let the MultiBit sync (although it might take several minutes and possibly as long as an hour or more) and you should be able to view the addresses contained in the .wallet file (even if it has a password).
EDIT: I tried to update Bitcoin Core, since I had the version from 2017. Thought maybe the new version might help me better, but for some reason, Windows won't let me install it. Says "blocked by your administrator," even though I am the administrator. Is that MalwareBytes doing that?
As per this thread on reddit:
https://www.reddit.com/r/Bitcoin/comments/m7rc5b/how_to_fix_bitcoin_cores_installation_error_this/It isn't antivirus related... it's a Windows code signing issue. Sadly, the Windows signing key for Bitcoin Core expired and the dev's were having issues getting a new one... because of this you get the stupid Windows 10 error saying that the application has been blocked. I ran into this issue a few days ago when install Bitcoin Core on a new laptop.
The solution was to use Win+X (or right click the start button) and then launch "Windows Powershell (Admin)"... you then have to navigate to and run the windows installer .exe from the admin powershell window...
Maybe... try to launch it "As Administrator', if it didn't worked, add an exception to your Antivirus.
For some reason... that doesn't work... but opening an admin powershell window and running from that does... Windows is "Awesome"