They're all breakable. One thing that will help them last seemingly forever is to put Unbreaking III and Mending on them. I've done that with Iron armor and it lasted a very, very, long time. My Chain armor with those enchantments almost broke during an intense battle with a horde of Drowned. I've never seen my Diamond armor get even close to 1/3 of it's durability used up.
I think the potion effects only apply to the players and other mobs.
Yeah I have heard that. I'm on Java right now and this is the first time I've played since 2015. Realistically I haven't played since like 2013, I was just a story line writer for an adventure map team in the latter years.