Seems like a lot of the things on the list are not definitive mistakes. Making a separate bracha on a dessert is certainly not universal if I’m understanding you correctly. The custom to have dessert after bentchen in order to get in another blessing is considered an extraneous bracha by some opinion.
“Not washing for bread the right way.” This is an interesting one. There seems to be a large portion of the uninformed masses who have adopted (probably unknowingly) the Chabad custom to wash 3 times on each hand before bread. I still wouldn’t call this “not the right way,” but there are a lot of people unknowingly following a minhag that isn’t really their own. But, that’s a topic for a different thread.
For an addition to the list: People waiting after eating something pareve because it was prepared on meat equipment. Also, people refraining from eating pareve foods which were prepared on dairy equipment when they’re fleishig.