I want to add to the other comment but also for you to be notified. You may have to enable the Canvas feature in the settings menu before you can use it.
There is a draw.io extension for VS Code (like another comment mentioned, it looks like the main application is vs code), and the UI elements inside the open tab with grid looks like draw.io's minimalistic dark theme.
It does look like obsidian to me. People like this or logseq a lot for their note taking. If you want a foss alternative, you can look at Joplin, though I can't recall if it has a graphing feature like this out of the box.
I'm fairly confident it's Obsidian, and not sure if the theme's even been changed, as the default Obsidian in dark mode looks the same. Not sure if Logseq uses the same icons like on the left, but Obsidian does for sure.