Apart from this with the feature of rectangular lasso there should also be an option to copy and paste it in another page or document

This. I think rectangular lasso is necessary.

Let us choose the lasso shape to be square like in Notability, this makes it much faster to select handwritings and move around on the page. It lets you just slide your stylus from the top left corner to the bottom right corner of a paragraph and select it rather than doing an entire circular travel around the paragraph.