Microsoft Word on Mac AND Updating Older Mac OS

I have an older Macbook Air 2011 that is still kicking. I have found that it is turning into a process to get into various web pages due to the OS being older. I bought a newer (used) Macbook Air 2017 (OS Monterey 12.4) to get a little more current (affordably) and to avoid the issues with web pages saying "The Connection Is Not Private." I also purchased a Microsoft Office 2011 Disc, good for 3 computers, with the intent of installing it on the 2017 Mac. Unfortunately it will not install because the OS on the 2017 Mac is not old enough for this version??? So now I am trying to figure out what to do because I need to either install Word on the 2017 Mac or install something else (ex. Pages) and convert hundreds of Word files (which I AM open to doing so long as it isn't too time-consuming or unrealistic of a task).

I would ultimately like to avoid using the free Word program that only allows for document use and storage through the cloud. I also am not interested in a Word program that requires a monthly or annual fee for using. I am not opposed to purchasing the right Office program so long as it will work for the 2017 Mac, but I really only need Word so it seems wasteful to purchase the whole Office setup when I won't be using most of it. So, I guess I have multiple questions.

1. Is there a way to get the authentic 2011 Microsoft Office program disc to install on the Macbook Air 2017?
2. If the 2011 version of the Microsoft Office simply cannot be installed on the 2017 Mac, are there any suggestions on what program I would need to purchase in order to get ONLY Word on the 2017 Mac?
3. Is there another program that would be comparable to Word, but free, that would allow me to easily edit and use my existing Word files without needing to convert every single on of them first?
4. If the Word files DO need to be converted, is there a fast and easy way to convert hundreds of files from Word to something like Pages (or any other recommended program similar to Word) in order to avoid going down the path of buying yet another Microsoft Office disc/program?
5. Off topic a little, but is there a way to update the 2011 Macbook Air (OS X El Captian 10.11.6) to a more current OS or get it to not constantly say every site is "not private?" Other than this issue, the computer is still fast and perfect for my basic needs.

Thanks so much for your time in helping me to troubleshoot this.