I put it like this:

sudo apt install postgresql postgresql-contrib

How to fix it?

Answer 1, authority 100%

First, what does the command do?

sudo service postgresql status

Remove everything

sudo apt --purge remove postgresql-12 postgresql-client-12 postgresql-client-common postgresql-common

Then

sudo rm -rf / var / lib / postgresql /
sudo rm -rf / var / log / postgresql /
sudo rm -rf / etc / postgresql /
sudo userdel -r postgres
sudo groupdel postgres
sudo apt autoremove -y

Then install

sudo apt-get install postgresql postgresql-contrib

Check

pg_isready

Should be / var / run / postgresql: 5432