Hide version history from external users (link sharing)

Barbara_EM 

Where exactly are you having problems?  The second option provided within the SharePoint Maven link is pretty detailed and shouldn't give too many problems.  On a high level you're basically creating a new group (which is a collection of users), then attaching a custom permission group to it.  Once these are done, you'll edit the permissions on the library level and add this custom group there. 

A step by step would (using content from the SharePoint Maven blog) be something like this: -

1. Navigate to the root (the very top-level site) of the site collection where your site resides
   Gear Icon > Site Settings
2. Under Users and Permissions choose Site permissions
3. From the ribbon, choose Permission Levels.  This is a screen that shows you all the existing permission groups.  Note it won't tell you where these are applied
4. To create a custom permission level, I suggest we just copy an existing one and adjust it slightly. So go ahead and click on Edit Permission Level
5. DON’T MAKE ANY CHANGES on the screen that appears next. Otherwise, you will mess up the out of the box permission level. Instead, just scroll all the way down and choose Copy Permission Level
6. Once the Permission Level has been copied, you can now make changes to it. Give it a name, you can also specify in the description the specifics of this custom permission level.  Next, scroll down to a list of specific permissions and un-check both View Versions and Delete Versions
7. Scroll down to the end of the page and click Create. Now, our custom permission level has been created!
8. The next step would be to apply this to a SharePoint User Group, either a new one or an existing one.  I'll assume that a new one is the best way for this.  So, using the cog --> Site Settings --> People & Groups to navigate to the People and Groups page.  This should resolve to People and Groups page (.../sites/SITE_NAME/_layouts/15/groups.aspx).  In here look for the New --> New Group action.  This loads a new screen
9. In this new screen, assign the name and description as required.  Make sure to scroll to the bottom of the page and assign the permission group you created earlier
   1. 
10. Once this has saved.  Click on Site Cog --> Site Contents.  This loads a view of all the libraries you have.  Hover over the tile for the library / list you want to amend and look for the ellipsis (...) to the right of the library name.  Click on this and select settings
11. In this new page, look under the the Permissions and Management header for Permissions for this document library.  This loads a new screen
    1. Permissions for this document library
12. If this library has permission inheritance, you'll see the group added here.  If not, you'll need to add the group via the Grant Permissions button.  You'll still need to add the relevant members to this group.

Hope that helps!

Barbara_EM 
Moving/copying documents around is bad. Fully agree.

The "CUSTOM PERMISSIONS LEVEL" approach should work.
One thing you should also check is whether the external users connect using OneDrive for Business.
If they use local copies and the sync has not yet run then they will have access to a previous version. Perhaps theoretical but something to be aware of.
Paul