I'm assuming you use windows since you are using Word. Knowing that, stay away from Scrivener. It'll begin operating just like word after a while with its bad optimization. It is primarily a MacOS program.
A near identical program for windows is YWriter. It's also free. Both programs have one hell of a learning curve to use if you want to go past the basics.
To answer your earlier question on Libre Office, yes, it's a free suite. No pay or annoying ads to prod you to eventually pay.
Now, for the main breakdown of responses you have received and will get after a while.
Notepad and similar programs are the equivalents of digital pen and paper. You type things in and it stays on there with no fuss. Better compatibility than most to transfer between your computer and the website you will choose to publish to.
Bundled writing suites like Word. Besides Libre you will be told about Openoffice, WPS, etc. They are like Word but come with limitations unique to each program. Word struggle to open some files (like you have found out) up to 512MB. On the other hand, something like Libre has reports at 10MB for their writer program. They also have a small learning curve. Mostly with things being placed in different areas compared to Word.
For the main crux of dedicated writing programs, i.e. for writing novels n'shit, it is the ability to have a much more user-friendly design of the basic Master Document that writing suites already have. I'm sure you'll see one vid of any of these options and be enamored at the idea of having different pages in a drop-down menu to the left or right of the main page. Writing suites already have this. They're just a pain to set-up. Or should I say, people are lazy in figuring out how to do it in a 3 minute search.
That's their main selling point. Every. Single. One. Drop-down or hidden menu has a place to "store" blurbs, character information, descriptions, ideas, notes, etc. Some have the ability to transfer the document file into a different format. i.e. .docx>epub>azw And those are good. You can also do that with an online file converter.
What I personally use is a mix of Word for editing. Formatting tends to transfer fine about 90% of the time. G.docs have a better time here.
A notepad program. Yes, A program. Any will do so I won't name one. It's for random outlining. I prefer it because it shows more compact information than Word.
Discord for when I'm out of the house and got a random pang of inspiration. Just make a private server and don't invite anyone if you use Discord. Copy/Paste is annoying with the timestamps carrying over. G.docs only when it's not being finnicky. That's why I prefer Discord for travel writing.
The actual writing is a mix between Ywriter7 because of sunk-cost fallacy in learning the damn thing and Quoll writer. I personally like Quoll since it can be both a dedicated writing program and a basic notepad at the same time. The difference is subtle but, I find it to be good enough. Also, I figured out how the whole thing worked in about 10 minutes. Compared to the pain both Scrivener and Ywriter made me go through. Only problem would be no dedicated night mode.
If you have hardware issues I suggest an update blocker or using the SH writing area and instead of publishing just save the chapter. Ventilation is great for computers. Run a virus sweep, clean caches, optimize, sacrifice a lamb to Tony, etc.