You’ve installed the python-dev libraries for Python 3. Your psycopg2 install is using python 2.7
If you want to use Python 3:
Make sure you’ve installed python3-pip
sudo apt-get install python3-pip
Then:
pip3 install psycopg2
If that still fails, try installing the development headers for postgresql:
sudo apt install python3-dev libpq-dev
pip3 install psycopg2
If on Python 2
sudo apt update
sudo apt-get install postgresql postgresql-contrib
sudo apt-get install libpq-dev
sudo apt-get install python-dev
sudo apt-get install python-pip
pip2 install psycopg2-binary
If on Ubuntu 20.04 or above
sudo apt-get install build-essential
Then run the other steps for either Python 2 or 3.