Work should be structured to be as non blocking as possible in the first place. If its not, there is either an issue in planning, resources, or in (unlikely) cases, truly it has to be serial, in which case it should be planned accordingly

I'd also argue, that 2 people being blocked because of X should warrant breaking through any focus period, as thats clear indication of an issue that needs more attention.

If you're talking about 2 people being blocked simply because they don't know what to do, thats why companies should have proper mentorship programs in the first place, it was a need hidden because being in-office made this less visible of a need, but it was always there, and dedicated mentorships are better than ad-hoc problem solving in these types of cases. Not every senior needs to be in the "deep work" pool (we do mentorship on rotation where I work)