Redirect part of a URL parameter to the URL-Path

I used a module that created links like this:

https://example.com/login?create_account=1&back=https://example.com/product/2164/?ets_rv_add_review=1

I need to redirect them to:

https://example.com/product/2164/

There are hundreds of these links.

I tried this but it's not working:

RewriteCond %{QUERY_STRING} ^create_account=([0-9]+)&back=([0-9]+)$
RewriteRule /login https://example.com/product/%1/? [L,R=301]

RewriteCond %{QUERY_STRING} ^create_account=([0-9]+)&back=([0-9]+)$
RewriteRule /login https://example.com/product/%1/? [L,R=301]

This tries to match a back URL parameter whose value consists solely of numbers, but your example includes an absolute URL (numbers are only in the last path segment). There are also more URL parameters in your example. /login would also fail to match in a .htaccess context since the URL-path matched by the RewriteRule pattern does not start with a slash.

Try the following instead, near the top of the root .htaccess file (the order is important):

RewriteCond %{QUERY_STRING} ^create_account=\d+&back=https://[^/]+/([^?]+)
RewriteRule ^login$ https://example.com/%1 [QSD,R=301,L]

I've included the product from the requested URL in the captured backreference (%1). This captures everything up to the query string.

And always test first with a 302 (temporary) redirect to avoid potential caching issues.