I have tested installs using php7.4 and no extra requirements are needed for installs on 7.4

MySQL8 support currently requires a bit of manual configuration outside of Ampache to install.

The newer versions default to caching-sha2-password as the default authentication plugin rather than mysql_native_password. MySQL 8.0 Reference Manual

For now it is recommended that you use the old default of mysql_native_password.

Update your mysql ini file

[mysqld]
default_authentication_plugin=mysql_native_password

And then update your root user.

ALTER USER 'root'@'localhost'
IDENTIFIED WITH mysql_native_password
BY 'password';
FLUSH PRIVILEGES;

After you install Ampache and create a database user for the site, you can reset root to an SHA2 password.

Until PHP 7.4 releases you won't be able to connect using caching-sha2-passwords.

PHP bugs #76243 mysql 8 - new default_authentication_plugin