You want to try something interesting but want to dual-boot. That last bit could be difficult or “impossible” but using a VM or running from USB stick are options.

• https://www.haiku-os.org/ I’ve run it from USB stick on some older laptop.
• https://chimera-linux.org/ FreeBSD user-land with a Linux kernel.
• https://nomadbsd.org/ FreeBSD which can be run from USB stick with persistent storage. Has a version with ZFS support.
• https://nixos.org/ Very interesting concept.
• https://www.gobolinux.org/ GoboLinux is an alternative Linux distribution which redefines the entire filesystem hierarchy. Doesn’t seem up to date but quite interesting. If I remember well you can have different versions of software installed at the same time. Let’s say (making this up) Bash 1.1, 3.1 and 5.2
• https://bedrocklinux.org/ Bedrock Linux is a meta Linux distribution which allows users to mix-and-match components from other, typically incompatible distributions.

Exactly.

True. And the “given enough eyeballs, all bugs are shallow” is a neat sounding thing from the past when the amount of code lines was not as much as now. Sometimes it is scary to see how long a vulnerability in the Linux kernel had been there for years, “waiting” to be exploited.