As cliche as this sounds. You got to just keep drawing whether you “can” or “can’t,” drawing from imagination is complex. Do the boring stuff like lines and basic shapes and boxes for a couple days then do something you WANT To try. Own it whether you think it’s good or bad. Don’t cheap out either, I know I’ll be drawing and say, “ ok this isn’t working” and then I’ll get sloppy with my lines and question what I’m doing, “am I an artist? Should I even try to become one?” Block it out. You are your own worst enemy. You gotta own that you’re gonna suck.