Installing Obsidian using Flatpack was difficult. I managed to install it using these 2 articles where I had to fix problems with Linux by “updating packages” (I’m not a developer):
If you are running Obsidian from Linux on ChromeOS, the folders you are storing data in need to be accessible to the Linux VM. (Linux on Chrome OS runs as a Virtual Machine, and file access is kept separate from the rest of the Chrome OS environment for security)
Open the Files app on your Chrome OS device, then navigate to the folder where your notes are (Probably somewhere in My Files, I suspect)
Two-finger tap on the folder name (acts like a right-click), or tap on the three dots in the upper right of the screen, to see the sub-menu, which should have the option: “Share with Linux”. Click on that.
Now that folder should be available for Obsidian to open.