Obsidian
Also on WindowsNotes kept as plain files on your computer, linked together.
Installs from Flathub.
Good news: Obsidian runs on Linux. It's the same app you use on Windows, and TuxPick installs it for you from Flathub.
Install Obsidian with TuxPickIt works on Ubuntu 22.04 and 24.04, and on systems built on them like Zorin OS and Pop!_OS.