Unable to add fields to forms

I was very unhappy with this issue as well, and without a solid response from Adobe, not too keen on the "Support Community."  I had a form that I had converted and programmed from Microsoft Word (2021) late last year.  When I tried to add form fields, they would simply disappear, no matter the type of field, during "Prepare Form" (Edit) mode (which is also not named very well as mentioned by someone else in this thread!).  I tried re-installing, I tried installing Acrobat DC on a different computer...Nothing.  It is clear now that the file got corrupt somehow, but it is clearly a bug that you can't work with a file that opens and is otherwise usable.  I had to go back and redo the whole form and then adding fields worked fine, just as it normally does.  But I lost 4 hours since it was a 7 page form that didn't auto-recognize very well at all.  Nightmare.

My sense is that no user experience experts were involved in this release of Adobe Acrobat Pro DC. This has really poor usability. I'm a seasoned expert at using these products and building forms.

But the processes of creating a form and editing the form fields are so much less intuitive than they used to be!

Example: I'd expect to see Edit Form on the menu or File + Insert Form + Checkbox or something like that from a menu. Nope.

Finding the Form Field Icons

Instead, the Form field icons are displayed along the top in the Prepare Form mode. To get there is a crazy path. See below.

Editing a Form (going back to edit)

Watch out if you close the document! You'll think you can never edit again. It takes a while to figure out, especially compared to the old Acrobat version. Here's how.

1. Choose Edit PDF. 
2. THEN on the right, way down at the bottom on the right, you will find an icon with a Wrench and a Plus sign. That's the More Tools button. (Don't confuse it with Settings; that's similar but different. Don't look for Edit Form; it's not there anymore. Don't check under the Edit menu. Not there either.)
   
3. Now you'll see a page of tasks. You'll see Prepare Form, but not Edit Form. To edit, you must choose Prepare Form. (This is extremely counterintuitive because you are editing -- not creating or preparing.) But this is what finally gets you there.
4. Now you will see the Form Field Icons shown below.
   
   

Using the Form Field Icons

Additionally, to use the form fields, or to insert,  you double-click to activate the checkbox for example and float it down to the spot on your page.

This is not Adobe caliber.

Tried that. May try a reinstall

What happens when you attempt to add fields?