As long as you’re using and plugging in your steamdeck reasonably often(every couple of days) the suspend mode is fantastic and there’s little reason to ever do a full shutdown or reboot in my experience. Boot into desktop mode the first time, and then just use the suspend mode to stay there, switching to gaming mode only when you want to play games. It also doesn’t take very long to switch from gaming mode to desktop mode or vice versa, I find the main time killer is the initial boot up into gaming mode the first time after shutdown.
Or you can just load games out of desktop mode, a recent update fixed a lot of the issues I had with the steam overlay not working in desktop mode and denying access to the powerful steaminput configuration options. That all works flawlessly now in desktop mode as well. I haven’t actually switched back to gaming mode for some time, since I use desktop mode to install games anyway and test the installation, it’s easier just to stay in desktop mode now.