LibreOffice is a good choice. It integrates with Zotero and does everything you need a word processor to do.
Another good choice is Google Docs. It also integrates with Zotero, and because it is cloud-based, it will automatically back up your work. It also makes it easy to work with others, since you can just share the document. However, your work is tied to your Google account, which will cause problems if you ever get locked out of it, and you sort of need an Internet connection to work on your stuff, which is not good, especially if you find you need to turn off the Internet to focus on writing.
Scrivener is what I use (see this page for details). I like it because it allows me to easily switch from one document to another, but you have to pay money for it, and until you are writing many things at once, it is unnecessary. If/when you get a job as a professor, it is worth looking at.
Overleaf is a cloud-based word processor that is built for writing in LaTeX. It is a little clunky to use and it is probably only worth it if you need to incorporate a lot of mathematical equations. Like Google Docs it does make it easier to work with others.
There are many other LaTeX solutions, and if you are inclined to write in LaTeX you are probably able to figure those out yourself.
There are Mac-specific options I am not familiar with, like Ulysses and Pages.
Via the Zotero plugin I use for Scrivener or through other options, you can also write in very simple software like Notepad, Notepad++, KWrite, Kate, Ghostwriter, Visual Studio Code with Markdown Editor, or Typora. The main obstacle is footnotes, but this can be overcome somewhat by Pandoc.
There are only three real options: do it manually, Zotero, or BibTeX alone. Doing it manually is a bad idea. It will take too much time, and the first time you need to change a paper from one format to another, you will regret it. BibTeX is only worth it if you write in LaTeX and you can use it in conjunction with Zotero if you want, via Better BibTeX. That leaves Zotero. Technically EndNote is an option, but the price is prohibitive.
I highly recommend Hypernomicon, which has a large learning curve but which is far more powerful and philosophy-focused than other options.
Other popular options include Obsidian, Notion, Joplin, and Goodnotes. You can also get by with a combination of PDF annotations and word processor documents.
My favorite is PDF-XChange Viewer, which is no longer officially available, but you can download it from here. Zotero’s built-in PDF reader is fine. Okular is generally very good, but it is a little annoying to learn. SumatraPDF is fine. Zotero, Okular, and SumatraPDF can open epub files too, which can be useful.
LibreOffice has a slideshow creator called Impress. If you use LaTeX, you can use Beamer. Google Slides and Canva are two cloud-based options.
Hypernomicon does this. Zotero also can do this. You very much want to have a clear, coherent, consistent system. Otherwise you will eventually end up with a situation you are not happy with.
I do not know a lot about the various options out there. I use MEGA, which gives you 20 GB free. Other options are Filen, which gives you 10 GB free, Dropbox, which gives you 2 GB free, iDrive, which gives you 10 GB free, PCloud, which gives you 6 GB free, and probably others as well.