No module named 'print_designer'

Why this error occurring all time

first, check app.txt under the sites folder

also check repository exists or not

Yes its there

First You need to check if app is installed or Not.
bench --site your-site list-apps

If you see print designer then run

bench setup requirements

This Basically will Install all the packages if not installed

(Optional) if Issue Remains Persistant

Run Bench Migrate
bench --site your-site migrate

adding @erpnapps,

then after apply the command:

bench build --force

after bench --site your-site migrate getting error

You need to install demo_app i think