In my opinion linux mint is most customizable . I have customized it like Windows xp,7,vista,10,Mac os . it has many themes that you can make you own theme . In Linux not only you can change the theme, but you can change the window manager or even code your own.

What is the most customizable Linux distro?

Debian has the largest collection of software repositories which makes it the most customizable. You can make Debian anything and be sure that it wont break. We have 129 distros listed on Distrowatch that are based on Debian to support this claim.

How do I customize Linux Mint 20?

But, it’s very easy to change the theme and icons in Linux Mint 20 without installing anything extra. You get the option to customize the look in the welcome screen itself. In either case, you just need to head on to “Themes” and start customizing.