DTLow

Evernote indicated pending expansion for the export options   
however this is expected to be HTML format   
Evernote's native note format is ENML, which is basically HTML
>>We (the team) will need to copy/edit/update all the files.
HTML files can be edited - your users can import into MS Word
 

Nope, web access is now counted as a device
 
 

The upgrade didn't delete the local legacy database (.exb file)    
- this stores your local notebook data
It will be accessed when you install the Legacy app and login

To prevent Evernote interpreting this as a list; insert a space before the checkbox

Make sure you're working in the Notebook page (click the Notebook icon in the sidebar)
Right-click a Stack

You can use the copy link feature   
This link opens in your account which is password protected
Screenshot is from my Mac after right-clicking on a note in the note list panel
There's also an option for a public link under the share menu
No password required to access

"All" is the default option
"Any" can be specified by prefixing your search arguments; example    any: tag:aaaaa tag:bbbbb

Install the Version 10 product; this will replace any previous Evernote version
Install the Evernote Legacy version
This will not impact your Version 10 installation
This will be installed as a separate app,  labeled as Evernote Legacy

Not clear about your reasons for updating your software    
I'm using the Legacy version with no issues

You can right-click a notebook and select export   
Personally, I'm using the Legacy version

Confirmed, you are accessing a support site restricted to paid accounts
All accounts can contact support via Twitter @evernotehelps  

Click on the tags icon to open the tag window
Hover the mouse cursor over a tag to get the ... 
Click on the ...
Click on Move tag

I also run Catalina; on an even older device
Deleting the app will certainly force a new download
First review the feedback in these forums before making a decision
I prefer installing from the Evernote web site (www.evernote.com/download)

reminderTime:* -reminderTime:day+1 -reminderDoneTime:*   
all dated reminders, exclude future dated, exclude completed
To also include undated reminders   reminderOrder:*

notebook:"client 1"     
with quotes

Which Evernote version are you using?
You're posting in the v10+ forums   
As per @Paul Meyers, I understand this problem has been resolved with the v10.0 release

Test drive would be the Basic account subscription
More bad new, The Plus subscription is no longer available   
On the plus side, Premium is available and can be subscribed on a monthly basis

Evernote Helper is working fine for me
You might want to contact Evernote Support (https://www.evernote.com/SupportLogin.action)

It's not an account thing - it's a notebook specification
You're posting in the Android forum   
With a Windows or Mac device, you can create Local Notebooks in your account   
This data in these notebooks is not sync'd to the servers, and remains on the specific device
Make sure you back up your data

I posted some Applescript basics at https://discussion.evernote.com/topic/112316-scripting-on-a-mac-applescript/
In your case, you want to select the notes and have the script process each one
The script code is   tell application "Evernote"   
                                        set theNotes to get selection
                                        repeat with theNote in theNotes
                                                                       < insert code here
                                         end repeat
                                    end tell
For the "simplify formatting" code, I searched the internet and found this https://developer.apple.com/library/archive/documentation/LanguagesUtilities/Conceptual/MacAutomationScriptingGuide/RemoveMarkupfromHTML.html
Feel free to ask if you have any questions implementing this

Evernote limits are documented here  https://help.evernote.com/hc/en-us/articles/209005247-Evernote-system-limits   
No limit on notes per notebook
I roll with a basically single notebook; 15k+ Notesj

It's actually  sourceURL:*

I"ll follow up on the Mac thing
In the meantime, we know the Mac data is a copy; the master data version is stored on the Evernote servers   
Update the shortcuts on the server using the web version at www.evernote.com   
The changes will sync to your Mac
 

Yes, you will be able to access (view) your data    
However, you will not be able to edit your oversize notes
Other plan restrictions are listed here https://evernote.com/compare-plans