I’m not sure I understand the question. Text files are perfectly fine for storing text data. It will be a long time before a computer can’t read a text file. What’s more important is how you store those files offline - a thumb drive, CD, DVD, external HD or online are all valid methods to keep the files. You should periodically make sure the media is still valid and you have a method to read them.
Are you asking if the data is secure? or if there is a future access issue? or if there are better options for what appears to be a logging usage?
FWIW I use a locked spreadsheet for the passwords. Separate sheets for various types of sites and users. I’m closing in on 150 combinations now.
Some malware types do fairly extensive scanning of all readable files looking for userid/passwords, CC numbers, SS numbers, etc.
LibreOffice is good for storing stuff like this if you use its encryption method. I’ve even got Mrs. FtG to use this so its not complicated at all.
Also, you never have good enough AV software. Brand new stuff is coming out all the time and AV makers are always behind. E.g., there’s a new “settings file” hole that is being exploited and no fix from MS yet. Nevermind AV makers.
I do use a dam password manager for important stuff. Like access to my financials. For other odd stuff, that I may need to remember, I will just drop in a .txt on my desk top. “You must be loged in here to use this” sort of stuff. Meh. I guess I’m lucky, I’ve never been a victim.
I am a bit pissed at the moment at Facebook. I NEVER use it, I all but SHUT IT DOWN. But I needed to use my Facebook login to see pictures of our dogs when we where away on vacation. Not MY account, I had to provide my login info at the kennels account to see the pictures.
And now, I’m getting ‘alerts’ of new messages from Facebook from every random stranger that happened to go to my high school 40 freaking years ago.
As we are in polite company at IMHO, I will allow the gentle reader derive just what I think of that.
It’s not terribly difficult for most people to remember a single password. Barring that, you write it (or some really good hints) down on a sticky note and stick it to the wall or the edge of your monitor, without any other context. The only way it gets compromised is if a burglar physically comes into your home and steals it, AND knows which password manager you use. If your passwords are in a spreadsheet on your computer like me and PoppaSan, then the burglar will also have to steal your computer (or find the relevant spreadsheet on your hard drive and make a copy). All of these are highly unlikely.
That wasn’t a serious question - I’ve been in IT most of my life, and I’ve done some work with cryptography.
FWIW, I use an offline password manager. I don’t trust the online ones.
For other sensitive things I use VeraCrypt. You can create an encrypted container of any size, give it any file name and extension, and save it in any location. It looks superficially like any normal file. Using VeraCrypt and a password, you can then mount it as a drive letter, and freely create and access content of any kind on that ‘secret drive’. It’s highly secure.