Ok, so we can use Tawk.to in 4.3 version? I didn't even tested to install it yet...
Yes, you do not need any plugin if you can change the code directly in root_head.cshtml. Place the tawk to script before </body> tag in that file, and then follow to add one line as mentioned below (referenced from the solution provide earlier in this forum post).
Also added following line on https://www.website.com/Admin/Setting/GeneralCommon: SEO SECTION -> Custom <head> tag:
<meta name="referrer" content="no-referrer-when-downgrade">
This should do.