My experience after upgrading from Win 7 to 10:
Things went fine for a few days - I left everything pretty untouched just to get used to the changes.
Suddenly, I couldn't drag and drop between panes in Explorer - got the old slashed circle symbol. Logged on with the Admin account and the problem wasn't there - so I figured it was a permissions issue with my regular account. Checked that account and nothing had changed. Checked to see if there were any MS updates - no.
In an attempt to change things up, I used Explorer's configuration tool to have it open with a different view (This PC). Next time I tried to launch it, I instead got an error message 'Can't find ". Please check your spelling ...'. Tried Start - Search - File Explorer - (launch)" and got a different error message, 'Can't find [[800fc67b0 ...' . Tried drilling down to the Explorer component of various Windows tools and they worked. It was just the direct launch that failed.
I came to this forum and found many older posts that described similar issues, but no real answers (Yes, I actually tied them all - spent an entire day at this because I use File Explorer a whole lot). Nothing changed.
It began to dawn on me that I was going to have to roll back the Win 10 upgrade and reapply it, but my instinct told me that this would in all probability only introduce a new set of issues. The next option was to do a reinstall of Win 10 over my current one, but while I was confident that my data would remain untouched, I fretted about the condition of all my installed applications.
It finally occurred to me that if my browser or word processor program was broken and couldn't be fixed, I would just switch to another, and that I should consider doing the same to solve this problem. Luckily, there are many alternative programs out there.
I settled on Explorer++ (Explorer++ - A small and fast file manager for Windows), as it is available for a donation of my choice and doesn't come bundled with a bunch of unwanted crapware. I installed it, chose the option for it to replace Explorer for all folders, and it seems to work exactly as advertised.
I can't close this without bemoaning the fact that there doesn't seem to be a way to report an issue such as this to someone at MS who can actually ask the right questions and get to the heart of the problem. I am a lifelong systems and application programmer, and my opinion is that even if the issue was caused by some random third-party vendor (seems unlikely, as it didn't occur until I used Explorer itself to change options), Windows users should have the means to recover without a complete re-install just for one misbehaving program.
So, if you're someone who can't get File Explorer to work right, you should consider using another product. This has worked out great for me!