It’s an interesting topic, Chivalry. I mean in the most literal sense it just means “horse soldiery”. Of course it has evolved into something much more. In truth, there is no record of any formalized ‘Code of Chivalry’ and much of what we think we know about the subject is filtered through the lense of poets talking about chivalry centuries after the knights had passed. In other words it’s largely based in fiction.
Still, I see it basically in the sense of an attitude of service toward God and Country, martial prowess, honour, courtesy and respect to all, and dedication to protect the weak and uphold peace and civil order. There is a built in humility and reverence for hierarchies. Importance is placed on knowing your place in those hierarchies and acting accordingly.
Holding doors, having good manners etc. is an element of this as it is or at least once was part and parcel with courtesy. However romantic idealism over the years has over-emphasized the importance of this facet of the whole IMHO, particularly in regard to treatment of women. It’s a pleasant notion but on its own not really the core of what Chivalry is/was.
I tend to be a door-holder where it makes sense. My wife enjoys this. Not every woman does. I try not to make a big thing of it. I see the passing of those social niceties as a very sad thing and try to do my part to keep them alive in small ways.
However Chivalry, to me, has as much or more to do with that attitude of service and being willing and able to do violence in defense of a person, a home, a nation or a set of ideals. The passing of this is sadder still as it is necessary for a civil society.