Boterham

You will probably have transformed into a monstrous vermin when you awake from uneasy dreams tomorrow morning.

I use VirtualBox, mostly because I started with that years ago amd had no reason to change. From what you described, it's capable of your project.

To be honest, VMs are probably the easiest way to do it, like many said already. You don't need to deep dive into virtualization to set up a few VMs and use them to learn about different distros. No need to think about how to partition your drive, mounting swap partition, disable hibernation... Want to try out another OS? Just create a new VM and you a ready to use it. You can simply create shared folders between host and guest and enable shared clipboard, if you want. Switching between the different systems is much easier than shutting down and rebooting another OS. You can even run them at the same time if you want and your hardware is good enough. And aside from the better convenience, the potential to break something is much less compared to tinkering around with a multi boot system, imo.

Everything is saved like on a "real" system.

I downloaded several distros in the last days and it was faster to download them then copying them on the USB drive. That felt weird.

An IQ of nearly 300 seems pretty galaxy brain imo.