How should I adapt my software's keyboard shortcuts for macOS users (e.g. when to use Cmd instead of Ctrl)?

I'm not familiar with macOS at all. Nevertheless, when designing cross-platform software features, one needs to be aware of such small differences. I've seen a lot of keybindings which are usually Ctrl+ (something) on Windows and Linux and Cmd+(something) on Mac.

For some standard actions (e.g. copy, save, etc.) you can easily find information on what the expected shortcut should be. However, when it's a software-specific action that's not so simple, especially if your software is some sort of plugin or component of a larger third-party program.
One can easily assume that Ctrl is equivalent to Cmd works as a general guideline, but does it really?

General question

When does this apply? When can I simply assume macKey = otherOsKey.replace('Ctrl+', 'Cmd+')?
For what keys or combinations? Or for what kind of actions?
I'm asking more in terms of good practice guidelines rather than an exhaustive list.

What I read about it makes it seem like ⌘ (Cmd) is similar to the WinKey, which I would think of as an OS-defined action that I'd probably want to avoid clashing with. E.g. maybe it makes sense for cross-app standard stuff like copy, save, etc. but not for some very specific action in my software?

Specific question

I want this particular feature to be on Ctrl+F1 on Windows and Linux.
Can I just use Cmd+F1 or should I expect it to clash with OS keybindings or a different expected behavior (because it's F1-F12 instead of a letter)? Should I use something else for specific actions of my app? This particular action would be a sort of "open documentation" action; but I'd like to also know what I should do in general.