nixCraft published a tutorial about installing Adminer on Ubuntu 20.04 LTS.
How to install Adminer on Ubuntu 20.04 LTS
Explains how to install Adminer on Ubuntu 20.04 Linux server as a web-based database management tool for MySQl, MariaDB, PostgreSQL, MSSQL, SQLite & Oracle.
How to install Adminer on Ubuntu 20.04 LTS - nixCraft