I am aware that usually one has to specify who is to benefit from one's Help action. However, when it comes to using it in combat, this comment by Jeremy Crawford says:
If you use the attack-aiding option in Help, the next ally who attacks the target gets the benefit.
However, maybe one wants to help a specific ally (e.g. enable a rogue to Sneak Attack) but initiative puts them much later in the round. Still, for some other tactical reasons, it might make next to no sense for the remaining allies to avoid attacking that target in the meantime.
Of course, one could argue that, as long as you can describe reasonably how you provide help to exactly that one specific ally without influencing the rest of the fight, something like this should be allowed. But I wonder if there is any explicit mention of this in the rules.
I've been referred to this extremely similar question: Do I choose the target or the ally for the Help action?
My main point of interest is the issue that is raised in the answer by HellSaint and the comments below it. Since this discussion is about a year old, maybe the remaining unclarities could be solved by more recent publisher's comments?
Thanks a lot for your help! (Horrible pun not intended.)
The Player's Handbook says on page 192, under "Actions in Combat" (emphasis mine):
From this, it appears that you can help a specific ally (but only their first attack gets advantage, if they have multiple attacks).