How to manage the loved one who has to have the last word

Why not use the slightly patronising comment "We'll just have to agree to differ"?

Or you could say “ well I would agree with you, but then we’d both be wrong “

?

Love this one!

I'd just smirk, put my hand up and sarcastically say "OK if you say so"

It isn't worth it as they are never wrong. I speak from bitter experience as my brother is like this. If he pontificates, as he often does, I ignore and turn the conversation.

How about, "Oh well, whatever works for you..." ?
But don't fall out with her over it! ?

In desperation I have said ‘I agree’ even if I don’t, stops the conversation totally as they’re flummoxed.

I usually say nothing and let it go.

My sister was very much like your Dil.
I would ask her if she just said so and so has died,she would look at me in a very strange way and say no,then i would say ok.
Not another word,well for at least a couple of minutes.
Kept me amused.

just use you mind to inwardly say the words that you really wanted to say. It is often better to keep the peace and keep the mouth zipped but no-one can read your mind and you can say what you want in there

My late FIL was like this ,I did used to argue with him until I realised he was just winding me up so I would tell him that he obviously knew better as he had so many years more experience .
Although I did still let my son have "girls toys and an umbrella" although FIL thought I was turning him into a "cissie" .
The 34 year old is a brilliant dad to his girls ,must be all those dolls he played with....lol

If it really got to me, I would say. We will just have to differ. Better be nice than right with people like that.