I’ve seen a bunch of posts about who Sherlock is texting in the closing montage:
There seems to be a lot of anxiety about this, that he’s texting Molly, or Irene, but this is a callback to ASiP, where he texted this to Lestrade:
They were just putting in as many “back to normal, solving cases” visuals as possible for this closing, IMO, which is why this was included. I came across someone else pointing this out last night in passing, and I wish I could remember who, but I can’t. Anyway, here’s a standalone post about it, since I keep seeing it come up.
(top screencap originally on a post by @ghislainem70, bottom cap is mine)