I've no problem with using LibreOffice for most of my document needs, but i haven't found a good substitute for microsoft's OneNote yet. I mainly use it to plan my RPG games and it helps a lot. What alternatives are there for organizing notes on linux, with similar features to those that OneNote provides?
I am surprised that no one has mentioned Rnote yet.
It is my favourite newly-created program for Linux. It is a relatively new app which supports annotating files and taking handwritten notes. You can import PDFs, set the page size to infinite or a fixed size (something OneNote can't do), adjust the background to display grids or lines or dots or nothing with any spacing you like, input text with your keyboard, .... It is available on Flathub for easy installation.
The only major downside is the following: Disclaimer: The file format is still unstable. It might change and break compatibility between versions.
It isn't open source, but it writes standard markdown files to disk, so I can switch programs whenever I like and I am not locked into the Obsidian ecosystem with my notes. That was the main reason why I decided against using Joplin, especially after my experience with converting recipes from Nextcloud Cookbook to markdown ...
In general I am always trying to find a simple file-based solution for whatever I need to do. I want to be able to sync it with Syncthing instead of something fancier that requires a centralised web server or even relies on a cloud service.
Amkng all note taking apps, FOSS or not, online and offline, Obsidian still holds the top spot unmatched. I don't even dislike to admit it anymore. It's just that good and really has almost everything.
Actually that's one of the main reasons I use Syncthing: It doesn't need a server, as it is a peer-to-peer architecture. Unlike a centralised solution (cloud storage, Nextcloud, etc.) devices sync directly with each other. If they are on the same local network, you get to enjoy the full bandwidth of your local network. If they need to sync over a long distance over the internet, you are limited by the upload and download speeds of your internet provider, just like with centralised storage.
I have a server that serves as an introducer, so I don't have to connect each device with every other device manually. But the server doesn't need to be available once all devices are connected with each other.
Syncing continues to work without it for as long as I don't reinstall any of the other devices. And even if I'd reinstall a device, I could delegate any other device to be the introducer or connect the devices manually with each other. It really is quite robust and fail-safe.