Linux

The parent comment mentions working on security for a paid OS, so looking at the perspective of something like the users of RHEL and SUSE: supply chain "paranoia" absolutely does matter a lot to enterprise users, many of which are bound by contract to specific security standards (especially when governments are involved). I noted that concerns at that level are rather meaningless to home users.

On a personal system, people generally do whatever they need to in order to get the software they want. Those things I listed are very common options for installing software outside of your distro's repos, and all of them offer less inherent vetting than Flathub while also tampering with your system more substantially. Though most of them at least use system libraries.

they added “bash scripts you find online”, which are only a problem if you don’t look them over or cannot understand them

I would honestly expect that the vast majority of people who see installation steps including curl [...] | sh (so common that even reputable projects like cargo/rust recommend it) simply run the command as-is without checking the downloaded script, and likewise do the same even if it's sudo sh. That can still be more or less fine if you trust the vendor/host, its SSL certificate, and your ability to type/copy the domain without error. Even if you look at the script, that might not get you far if it happens to be a self-extracting one unless you also check its payload.