Key Steps:

1. add-apt-repository universe; apt update & upgrade
2. create odoo system user
3. create postgresql system user
4. apt install postgresql
5. create user in postgresql, i.e. odoo
6. install basic software
   1. python 3+ with required packages : nodejs, npm, build-essential, etc
   2. using apt install better, werkzeug=1.0.1, PyPDF2, reportlab
      1. using apt install python3-werkzeug better as it’ll install dependencies
   3. using the requirements.txt inside the Odoo distribution for install packages
      1. after Odoo 13, nano requirements.txt add psycopg2-binary==2.8.6
      2. pip install -r requirements.txt
   4. in particular, wkhtmltox via git clone deb and apt have it instal
7. create directories for odoo
   1. installation root e.g. /opt/odoo
   2. var/log
8. git clone odoo branch 14
9. touch /etc/odoo.conf
10. cd /opt/odoo/odoo-server; ./odoo-bin -c /etc/odoo.conf
11. using browser connecting to :8069 as trial
    1. give password
    2. create the first database & login
12. make start odoo as service
13. setup nginx as reverse proxy and hide port 8069 from url

Source:

Install Odoo 14 | Installation of Odoo 14 On Ubuntu

https://techtutorguro.com/how-to-install-odoo-12-on-ubuntu-20-04/