First, there are many gaps in pretty much every home. Junctions between drywall/plaster joints, windows and window frames, every electrical switch/outlet box, details in the attic and roof, the rim joists and sill plates, and yes, even any exposed masonry.

Secondly, exposed masonry does often warrant being air sealed:

https://www.greenbuildingadvisor.com/article/insulating-old-...

https://www.jlconline.com/how-to/insulation/air-sealing-a-br...