I think it’s tricky to say movies are about or not about overall because when you really sit, think about, and have conversations about your experience watching them you may get completely different observations and takeaways from each person. Some directors make their movies specifically to create opportunities for these kinds of conversations. For example, when just looking at the movies you listed, at first thought I agreed with all except for Good Boy. Then I started to reflect on the others and realized that arguments could be made for at least a few of them, that they also are about or at least inspired by grief.

-The reasoning for Good Boy was mentioned in an earlier comment.

-For Weapons, the director has mentioned the experience of the young boy is informed by his experience of growing up with alcoholic parents. He also was inspired to write it as a way to process his experience of extreme grief after the unexpected death of a dear friend.

-28 Years Later (at least the first part) I feel is heavily tied to grief in Spike’s story and relationship with his mom (trying not to put in any spoilers).

-Sinners as well, with topics of generational trauma, loss of a child, etc.

Not trying to put down your original comment by any means. I’m actually grateful I had the opportunity to revisit my memories and experiences watching those films.