What you are asking for is impossible, and if SEO consultants are asking for this then they do not know what they’re talking about. WordPress is not redirecting you to a non-slashed homepage, the change happens before your browser even starts the request.
To understand why, take a look at one of the most basic HTTP requests possible:, a GET request to retrieve the root of example.com:
GET / HTTP/1.1
Host: example.com
This requests the root of a domain, but there is no way to remove the / here. If I delete it then I will be sending an invalid request to HTTP/1.1 with no protocol version afterwards.
Likewise, if you try to inspect the HTTP network traffic, you will see no redirects from example.com/ to example.com because they are the same address. I don’t mean that they are equivalent, or that they lead to the same place, but that they are 100% identical. The display of the / is purely the browser being helpful, which is why visiting example.com/ in the browser will show example.com in the address bar. Being able to put a trailing slash on a root of a domain is a happy accident of how the URL spec works, and one that browsers remove to simplify the URL.
What you are asking for is impossible, and is not how HTTP works.
As a further test, you can prove this yourself:
curl -s -L -D - https://example.com -o /dev/null -w '%{url_effective}'
Run this, then run it again with a trailing /, and the output is identical. There is no redirect, and WordPress is not involved, this is much lower at the foundation of HTTP.
If you’re still in doubt, try to find an example of a site that has a trailing slash in modern Chrome.