Drupal 8.x

I am looking for some overall implementation advice. The system I am working on has about 30-50 taxonomies.  We didn't want to add a field for every taxonomy since the editors would have hated that. Initially we went with one field called "search terms" that let them reference multiple taxonomies.  Two things are not yet solved: Making a great entity browser for these terms and making them all available as separate facets while they are in one field. The first should be easy enough and I will work on it today.

Might be a straightforward question, but is there a way to "unset" a twig template being used by a parent theme i.e. revert back to the system template?

The template in question is block--system-menu-block.html.twig

Just seems a bit messy to copy the system block--system-menu-block.html.twig into my sub-theme. 

Putting this up here because I had to a complete site rebuild, and this might help others. (I also can't for the life of me find out how to document it more formally).

Cause - I couldn't find a way to use Lockr to encrypt the registration email. So I used Dbee. 

My Error

I used Dbee to encrypt email addresses, to comply with GDPR.

I then set Dbee to use the Lockr key, for added security. 

Problem

When you Move to Production, whatever else you do, User 1 Email remains encrypted.

This BREAKS the Move to Production.

I've been googling and not found a clear answer.

I set up a new D8.9 site

Then upgraded to PHP7.3 (to play with D9).

Then realised I needed to add a Module to the D8 site. Redirect on Login.

Composer failed - allow_url_fopen was OFF.

I went to WHM and changed it to ON, and installed the new module.

(I looked at my PHP7.0 set up, and allow_url_fopen was ON, hence no problems previously).

However my googling made it is clear that allow_url_fopen ON is considered a security risk.

QUESTION