Confused about syncing bookmarks

I am using Edge on two laptops, one in UK and one abroad.
I understand if I turn on sync on one laptop my bookmarks will be stored by MS in the cloud.
But what happens when I turn on sync on the second laptop ?
Are the current bookmarks on it overwritten from the cloud - or are they all merged together - or do the current ones upload and overwrite what is in the cloud?
Nothing is properly explained in any MS missive as far as I can see.
Thanks for any advice.

Windows 10 Home 20H1

They merge. At least on Chrome they do, and Edge is based on Chromium, so I would think they'd do the same. I found they don't merge well though (I had many duplicates, but maybe it's changed since I tried the merge/sync a couple years ago), and found adding all bookmarks under one browser before syncing is best. Then on the other computer you want to sync just make sure all bookmarks are deleted, and then turn on sync, and everything will sync correctly, and you'll have an exact copy on each computer.

Thanks Bobby, I will certainly try that when I am back abroad (hopefully!).

In Edge there is a "Remove duplicate favorites" in bookmark settings so that might work.

I have been using a Chrome extension (in Edge) called Eversync (FVD Synchronizer) for a while now which will upload to a server or download from it or merge bookmarks - that's fine but you have to remember to keep up to date.
I am now on the laptop abroad and have just downloaded the bookmarks that I had previously uploaded on my UK laptop so I am fully confident that my bookmarks on each are identical.
I am now going to turn on sync in Edge which should keep things identical in future.
And I am going to do the same in Chrome itself.
I am just hoping that when I turn on sync in the UK it doesn't merge and double-up everything.

- - - Updated - - -

Well, that was a complete disaster !
Sync in Edge here gave me 1598 bookmarks, around one third of which I had spent ages deleting in the UK.
Obviously it picked up an old set from sometime when I had tried to sync before but since turned off.
Thanks a bunch Microsoft - of course you always know best what I want !
Never mind, resolved using the trustworthy Eversync again.

If I turn on sync in the UK, I presume the same will happen again - so what's the way forward now?
It seems I need to correct/overwrite what's on MS server, that is do what Eversync does but MS seems incapable of.
Is there any way to do it?