Marriage

Ditto.

But me and DH don't keep bathroom habits secret - the door's always open and we generally give commentary on notable happenings 😂

Of course, it's just a bare minimum thing.
There's no happiness with a cheater or general shit quality man though.

Good, but difficult question.
My parents were married for 60 years and had a really friendship/partnership marriage, where they both supported one another, took decisions together etc. etc.
I have numerous friends, who have been married for over 40 years, again, friends, equal partners etc. etc.
You need to find someone you get along with and also fancy and the feeling has to be mutual. Not so easy these days.
Joint thoughts on things like careers and children.

I can't comment on whether it's cultural or not, but what you're describing ("no flirting to a point of exchanging texts, cheating, secrecy, or any of that") is what I would consider a very normal marriage.

The only secrets I have from my husband are what I do in the bathroom and what I spend on his birthday present. I'm confident that the only secret he has from me is what he spend on my present (because I know far more than I would like about what he does in the bathroom).

Yes it’s possible and what everyone should strive for in a marriage. My son borrows my phone every other night for a dog walk and I used my husbands phone in that time last night, there was no worries about ‘finding’ stuff because we are completely upfront and honest with each other. I wouldn’t have it any other way

😂😂😂

Yes. Mine is like that.

1. I chose the right man - one who wanted to live the same way as me.
2. We discussed everything practical before we married. Finances, chores, religion, parenting style should we have children, our boundaries when it comes to cheating (does porn count, does staring at someone else count etc).
3. Because the man I chose was completely honest (I had never seen or heard of him lying even to someone he disliked or to get himself out of bother) I knew that meant what he said about everything in point 2.

Of course that's possible. That's what a healthy relationship should be. It's certainly what mine is and many of my friends have. Seems like a bare minimum really to trust your partner and not have to worry about cheating and deceit.