The plan is actually ingeniously simple: to try out the latest Ubuntu, Manjaro or openSUSE Linux, install it on an external SSD. If you don’t like the distribution or drivers are missing, delete the SSD again and try the next distribution – or simply boot your usual operating system from the internal hard drive or SSD. If the external drive is not connected, there should be no indication of the test installation.
In practice, however, some distributions leave traces on the internal mass storage of your PC even if you install them on an external drive. The crux of the matter is the EFI boot loader for UEFI firmwares: so that the boot order in the mainboard firmware does not have to be changed, some distributions such as Ubuntu 22.10 install their boot loader on the EFI partition of the internal hard drive and also use it as a standard -Boot loader on. If the external drive is missing, the bootloader of the distribution installed as a test starts, but can no longer find the kernel. So if you’re trying out the just-released Ubuntu 23.04 on an external SSD and want to make sure it doesn’t make any changes to your hard drive or SSD, you can hide them from the installer.
The easiest solution is if your machine uses an NVMe SSD internally. You can easily determine this by booting, for example, Ubuntu 23.04 from the USB stick or your already installed Linux and then in the terminal with the command
lsblk see what drives are there. If the SSD has a name like nvme0n1, then it is an NVMe drive. For this is the kernel module
nvme responsible. If you blacklist this module when you start Ubuntu 23.04, for example, you deny the installer any access to these drives – they are not even initialized.