Most, as far as I'm aware, since it's not required to do the work in almost all cases.

I can only speak for the U.S., but "required to actually do the work" has nothing to do with whether or not I'm legally allowed to set a requirement for a job.

There are protected classes/categories that can't be part of the employment decision, but outside of those, the employer is free to set whatever criteria they want for the position.

If I run a plumbing company, I could say "all of our plumbers must have a computer science degree," and I can't imagine there's any legal reason I couldn't do that. I'd certainly have a recruiting problem, but not a legal problem as far as I'm aware.

If the requirement has a disparate impact on one of those protected classes, you can run into problems in the US.

So in the case of plumbers, if a plaintiff can show that you are hiring fewer women because women are less likely to have CS degree—then you would need to show a “demonstrable relationship to the requirements of the job” for a CS degree.

However, this isn’t an issue for software developer positions. A CS degree doesn’t have to be absolutely necessary to be able to perform the job, it just needs a demonstrable relationship to the job requirement. There is also already precedent that a degree in a related field does meet that requirement.

That’s not how that works at all. There’s clear precedent that employers are allowed to require specific degrees.

In fact, depending on regulations, it can happen that you end up with somewhat junior team member having to sign off on all materials because they are the only one with necessary accredited title...

For certain (or certain kinds of) positions, yes. That's the "almost all" part.

There’s no problem with requiring a CS degree for every single software developer, software engineer, programmer, or coder job. Since those are the kinds of jobs that were obviously being discussed it’s not “almost all”, it’s essentially none.