Manners, like everything else, change in the course of a generation, or so.
When I was a child, up to around 1960 men and boys automatically took of their caps or hats when coming indoors, or greeting a lady in the street. A woman kept her hat on in restaurants and when visiting friends in their homes during the day, if she belonged to my grandmothers' generation.
Then we all stopped wearing hats and by the time it became fashionable for boys to wear baseball caps, the lads who did so, had never heard it was impolite to wear headgear indoors.
Putting your elbows on the table was most definitely considered bad manners in my childhood, where manners were not just a matter of saying please and thank you, but a standard of general polite behaviour.
Manners covered all aspects of life, but they change. My grandmothers had been brought up never to speak to an adult, unless spoken to. My generation wasn't, but we were taught to rise in buses and offer our seats to grown-ups. Today's children aren't, as a rule.
I remember the brother of a schoolfriend of mine rising whenever any adult came into the room where we were. He was the only boy I knew who had been taught to do so, and it really won him points in the eyes of my great-aunt, to whom it had been a commonplace of good manners in her youth.
Personally, I draw the line at mobile phones and lap-tops at the table during meals. I expect people to eat with their mouths closed and their elbows off the table and not to put their knife in their mouths, and while I taught I did ask pupils not to wear sunglasses and hats in the classroom.
Oh, and at the beginning of the lockdown I offended a friend, who had been reproved in a shop for not covering her mouth when she coughed, by remarking that I too would have requested her to remember to do so.