Guild Wars 2

I heard mmr can drop when you dont play for a while
and I would like to understand this mechanic.

Does this happen for each class individually or for your whole account?
If I dont play on class A for a while but I do play on B. Does mmr still drop on class A, while I play on class B?

In both ranked and unranked?
Does this drop significantly in short time?

Lets say I play only in the weekend for a while. How much does it drop, in the 5 days or so in between weekends? Tiny bit, significantly, a bit in between?

I’m pretty sure there has never been MMR decay. Not even in the old system, all that did was drop your rank.