Steps to reproduce the issue

install Joomla 4 with a db prefix of jos_ - complete the installation.

delete configuration.php

install Joomla 4 with a db prefix of jos_ - complete the installation

Inspect database - note new tables prefixed bak_jos_

Make a known change in a table with a prefix bak_jos_

delete configuration.php

install Joomla 4 with a db prefix of jos_ - complete the installation

Expected result

No existing tables with a bak_jos_ prefix are OVERWRITTEN leading to data loss.

Installation to fail if existing table exists

Expect to be asked if I want to backup or remove existing tables like Joomla 3

Actual result

Note you are never asked (like Joomla 3) if you want to backup or remove existing tables. They are backed up regardless if found.

any existing tables with a bak_jos_ prefix are OVERWRITTEN leading to data loss.

System information (as much as possible)

Additional comments

Joomla 3 screenshot from documentation