I despair of these MILs

There are two sides to every story and we only hear one side in here.

Nobody is saying they are. A significant minority do seem to be like this. My own was overbearing and unpleasant to all of her 5 DILs. Not one of us shed a tear when she died. We had all had her as MIL for at least 20 years, some of us for 40. I find it shocking that none of us were sad. I've never not felt sad about anyone else's passing.

It is great that you are wanting to have a good relationship with you DIL, I think you are amazing for wanting this. My own MIL I now have no contact with and neither do my DC as she was just so awful to me. All the best OP

On here you will only have the bad. People won’t make threads about the good. My MIL is fine. Not amazing but no issues. She leaves us alone, no interfering, but i don’t have any inclination to spend time with her either. Suits us fine!

The overwhelming majority of MILs are fine. But that doesn't make for very good anecdotes on social media.

Not all MILs are like that

I am a MIL and have a MIL. I use mine as a guide to how not to treat my DIL. Most of my stories of my MIL are far too outing to go into detail but she has cancelled holidays we were due to go on to stay with family members, ringing to say DH couldn't get time off and arranged for her and friends to go so we couldn't.
she tried to sit in my seat at DS's (her GS) wedding (I had a reserved place with my name on), an usher had to force her to move. This was after threatening to boycott because she wanted certain people invited.
We had a tiny wedding planned (we were pretty broke and just bought our first home). She said she wouldn't come if we denied her a much bigger wedding. I was young and naive and DH knew no better so we agreed. She got her wish, didn't contribute and never even gave us a card or gift.
I wanted my bouquets putting on my GM's grave. On return from honeymoon I found out she'd taken it from my aunt. I have hundreds of stories like that spanning decades. I'm now very low contact and do nothing for her. She believes she's the matriarch of her family and should be the primary consideration in everything.

I get on with my son in law and daughter in law just fine :)
But then I am a normal person, not trying to control anyone or anything. I look after my grandchild (and will be at the birth of no 2 if all goes well.. ) and both SIL and DIL lived with us for a few years and it was lovely... I miss the happy chaos!
I've never demanded time with my grandchild... however I am the main child care and now they ask for sleepovers if I haven't had them for a couple of days.
I've never flounced in my life

I'm sure the majority are sane normal people, it's just the batshit ones get posted about!

Not all MILs are bad - and not all DILs are good! We only hear about the bad mothers in law - there are hundreds of mothers in law who are supportive (and very useful!) .

Not another MIL, you do know like other areas of humanity some are good, some bad and some are ok. They are not all of the same ilk.