If you have a mouse connected to your Chromebook, you can right-click the typing area instead of double-tapping the trackpad.
If the keyboard doesn’t open, just tap any typing area to launch it. If you want to use the on-screen keyboard without tablet mode, you can enable it in your accessibility settings. Here’s how: Click the time at the bottom-right and select Settings. Click Advanced. Click Manage accessibility features. Select Enable on-screen keyboard.