reMarkableWiki

Their isn't an option by default to draw simple shapes or straight lines, but you can get something simillar by using one of these methods.

Lamp is a config based event injector used to inject finger or stylus events. This allows you to simulate a circle, square, line, … drawing. You can use this in combination with genie to quickly draw a shape with a gesture.

You can use a tool like remarkable-layers. You can make a pdf with the shapes you'd like to have, convert these to the lines format from reMarkable and store this as a notebook on your device. When you need a shape, you can open this notebook and copy paste it from there.

You can also use a ruler.