I solved the problem. I have to do this in order to be able to install v8.x.x
cd /home/frappe/frappe-bench
bench switch-to-branch v8.x.x
bench update
.env/bin/pip install --upgrade pip==9.0.3
.env/bin/pip -q -e ./apps/frappe
.env/bin/pip -q -e ./apps/erpnext
bench migrate
I have to do that for v8.x.x and v9.x.x. For v10.x.x is compatible with pip 19.x
How do I change this thread to solved?