I've trying to build actionable notifications in Node Red to push to Home Assistant, but all I get it just normal notifications with no actions or clickable option.
I'm not clear on what you mean by this, do you have a link? If you want the texts to show up instantly you need to use the interruption level option in the data section.
You need three {{{}}} around the payload. By default, Mustache will replace certain characters with their HTML escape codes. To prevent this, use triple braces: {{{payload}}}
I don't have an iphone so I haven't seen this issue. However it seems that this is just the way iphones work, especially 3d touch enabled devices, from the docs
iOS 13 and later
All devices support notification expanding by performing a right to left swipe and pressing 'View' in the lock screen or pressing and holding, but on 3D Touch-enabled devices you may still need to apply some force to do it. If you're not in the lock screen, you can also pull the notification down to expand it.