The title and picture say it all. It's a very subtle texture.
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That looks to me like a texture that developed over the years, inadvertently, with application of multiple layers of paint using a nappy roller.
You could try to duplicate by spray texturing in a "small blot" pattern, then knocking it down with a low nap roller. There are probably other ways... maybe a stippling roller would come close.
Bottom line is there is no way to really perfectly match any texture. Even pros need lots of practice and trial and error...