Can I be sure LL installer will not affect whatever boot process windows has?

[wofoo]

For context:

This is a desktop with win 11, and secure booth enabled. I've read the recommendation is to disable it, but I don't want to break anything as this is my main machine and I need it operational. If installing LL would bork windows, I'd be in trouble.

LL will be installed in an external, USB 3 1TB SSD drive. The whole point of this drive is not to have to touch anything with the existing setup (partitioning, resizing).

I've used linux for years. I know full well how easy it is to bork things. This is why I'm asking first here.

I did a trial on an extra laptop, which had an internal SSD running two linuxes under grub (solus and void). I did the install on the external SSD, and guess what? the machine didn't boot at all when selecting the internal drive. That is LL install process might have affected the internal SSD (is this possible?)

With this experience, I'm very wary to set it loose on my main machine.

Is there any other possibility? Did the installer fail, or was this user error?
I ran it from the external SSD, tested nvidia, external monitors... everything I'll need for the desktop (except it has a more recent nvidia 3090). I'm being careful as you see.

[stevef]

Can I be sure LL installer will not affect whatever boot process windows has?

Even if someone reading this had exactly the same set up and had successfully done exactly what you propose it is not guaranteed that your outcome would be the same.  Dual boot actually requires some change to the machines boot process so to some extent you *need* to change the W11 boot process even if it is done in UEFI.

In your trial, the starting points have different hardware and OS.  If you'd had success it wouldn't really translate to success with a desktop W11 machine.  It appears something went wrong with the trial but, with the information provided, trying to guess what happened would only be speculation.