I don't hate snap as much as some people but I do usually prefer not to use it so it's really annoying when I: apt install and it just installs a snap without asking, is there a way I can prevent that, either by making it ask or by just failing.
I don't want to remove snap entirely, just stop apt from installing snaps automatically or at all.
If you remove snap, then you can pin it so that it is never installed by another apt package (e.g. chromium/firefox).
If you don't remove snap altogether, you can't prevent apt from running snap in the backend, because snap is already installed.
However, you can read the description of the package in https://packages.ubuntu.com to figure out whether it is a dummy package for snap. For example, both Firefox and Chromium debs say that they are dummy packages.
Alternatively, run apt show firefox to read the package description.
So, read the description before you install anything.