not 100% sure but I could imagine you might not be able to go v7 > v11 directly but rather need to do v7 > v8 > v9 > v10 > v11.
that would include doing bench switch-to-branch v8.x.x frappe erpnext --upgrade cycles until you get to the master branch again.
bench switch-to-branch v8.x.x frappe erpnext --upgrade
bench update --patch
bench setup requirements
bench --site [your-site-name] migrate
bench restart
… and so on through all the intermediate versions until you finally reach master (v11). As mentioned I am not 100% positive this is the way to do it, so maybe can someone else confirm what I am saying is the way to go?