The abstract doesn't say that isolation is negative (I think). It just says WFH folks are more socially isolated.
For some people, more social isolation is OK. For others, not so OK. YMMV .
I personally think that more socializing is better, if it's with people who I become better by being around. The tough part is knowing who's good for me, and how I can find them.
True, I meant forced socialisation a.k.a office. You need some socialising most days but most people get that from living with spouse/family/room mates etc i.e. people they have chosen.