I don't think the issue is that people are hiding the fact that their WFH situation is not ideal. The people who have crappy WFH setups are quick to tell everyone. They aren't trying to get away with working from home, they are asking to work from an office.
Even if you have this WFH certification like you talk about, that isn't going to tell your employer much. Some people will have great WFH setups and not be very productive, some people will have bad setups and do great work. The only way to see which is which is to observe their productivity. Certification won't help.
It doesn't really seem beneficial. In the end all that actually matters is that the employee is sufficiently productive. There's no reason to needlessly gatekeep working from home. Everyone works differently so whatever standard that gets set might work for a few people but be less beneficial for others and basically useless for another group.
Do we really want SWE interviews/applications to get more toxic than they already are? On top of quizzing for largely non-pertinent academic knowledge, wasting people's weekends with no-pay projects to "judge their work", and other arbitrary BS do we also want to tack on a qualification for getting hired being that your home is structured in an employer approved way?