grml, the sysop powerhouse standing on Debian's giant shoulders, is my go-to distro for diagnosing/fixing all kinds of broken computery things for what has been much more than a decade. Be it hardware/hosts that are acting up, or broken GNU/Linux installations of all kinds - grml offers all the tools that can help make things right again (or at least arrive at the definite conclusion that stuff is FUBAR ;)).

We've recently started using its commercial sister project, grml-forensic (https://grml-forensic.org/) at work, and my colleagues in forensics love it!

I highly recommend everything the grml devs touch :)