I wanted to configure a Cinnamon desktop that used optirun so I created a new .desktop file in /usr/share/xsessions.
However, this option is not being shown as a desktop on the login screen. I've tried killall lightdm and also restarting the computer.
What do I need to do to get my new desktop to come up as an option?
The reason was because I had a command with args in Exec and TryExec rather than the path to a script.
Reading this post shows that TryExec isn't actually executed and it is just used to decide whether to offer this desktop, so that could be the reason it didn't work for me to start with.
Solution: Ensure TryExec and possibly Exec point to actual script file paths rather than stating an executable with args.