I'd like to know if there is another way other than holding the shift key to draw a straight line on iPad Pro using Photoshop? I have been trying out a way to do it but... I'm unsure if such command is even available(????)
Are you asking for a particular reason? Are you just curious or are you facing a specific problem? If you are having a specific issue it may shape some of the answers.
The following method involves the Pen tool. Hope it helps…
Use the Pen tool to draw a path that includes as many straight and/or curved segments that you like.
Switch to the Brush tool.
With the Brush tool active and the path active, select the "Stroke path with brush" button found at the bottom of the Paths panel.
Bonus tip: If you hold down the Alt/Option key while pressing the "Stroke path with brush" button, or you choose "Stroke Path" from the Paths panel menu, a dialog box will open that allows you to "Simulate Pressure" when you stroke the path.