Use it for a month or two and decide it's not for you.

That is in between "use it for very short period of time" and "use it forever"

Using a regular mutable system and Nix on top using Home Manager for example.

Gobolinux comes to mind.

If you don't mind a very limited set of software, the way tinycorelinux is setup can also allow multiple different tcz installed

These two Linux distros essentially allow two different versions of same software/libraries (glibc/python whatever) installed

(Gobolinux explicitly states that whereas I find it to be an unintended but elegant consequence for tinycorelinux but I recommend taking a look at Gobolinux)

Using it for a year or so and then try another OS is my guess