The worst issue is that all my existing InDesign documents won't open through file explorer and need to be opened from within the new InDesign
This could be a File Association issue - check your operating system and search the internet how to associate file types with the correct application.
There are various reasons when installing a new program why the file types associated with them are not linked correctly.
even then some files are corrupt and can't be opened at all.
This is odd - and I've seen others mention this too.
Your best bet is to keep working in the previous version of InDesign - if it's deleted or removed from your system you can still reinstall it .
https://helpx.adobe.com/download-install/using/install-previous-version.html
If you want to work in the latest version with this file that appears to corrupted
Open your document in the previous version of InDesign.
File>Export and choose IDML
Open the IDML file in the NEW version of InDesign.
Why does this corruption happen... new updates to new programmes might shift some 'logic' in the file structure.
InDesign for all it is is a collection of plugins/panels - think of it as a giant database and when a new feature is added it might shift some of that data to different datablock - so when you open your old document InDesign might be trying to fetch data from an area where that is not there anymore.
I have to admit - this has never ever happened to me in 20 odd years of using InDesign .
But I've seen more posts about corrupt files lately.
Your best bet is to keep working with projects in the application you first started them in.
If you want to move to the new version - then do the IDML export I mentioned earlier.
It also erased all my recent document history and I can't access the latest files I had open that were meant to be in my creative cloud files.
Your recent document history is linked directly to the application usage. You never used this new Application - so you have no recent history. It didn't delete anything - you simply don't have a recent history in the new Application.
Your creative cloud files should all still be there and in tact - installing a new version of an application does not affect your Creative Cloud files.