Adobe illustrator why can't I draw with a brush?

Question

Adobe Illustrator

I saved the svg file earlier, today I wanted to open it to edit it, but for some reason the brush does not work on the cursor, a small circle with an intersection is visible, maybe I didn’t set something correctly somewhere?

Answer 1

When saving via "Save as" there is a checkbox that makes it possible to edit this file later "Preserve Illustrator Editing Capabilities" (Save editing ability). Otherwise, the SVG cannot be edited after saving.
Working files must be kept in .ai or .eps - any editable format, and the final result should be exported to final .svg, .png and others.

Answer 2

Perhaps you need to select a layer first?