I sometimes found that the setting in the Settings > Permissions > Customer Account could be missing in Odoo 16, when I follow Marc Schultz's instruction, install the eCommerce App. , and go to the website app settings -> then in "Shop - Checkout Process" set the "Sign in/up at checkout" to Disabled (buy as guest), it works. But I don't want eCommerce App, so I remove it, surprisingly, the Settings > Permissions > Customer Account => Change this from "Free sign up" to "On invitation" appears again! 

in Odoo 16 you can try to hide the sign in button Edit > Click on the menu > Customize

Found the solution. So, here for future humans who land here:

Settings > Permissions > Customer Account => Change this from "Free sign up" to "On invitation"

Version 16

This is what I have found through testing to accomplish the following:

1. Don't allow public registration

2. Don't allow checkout as guest

3. Maintain use of the Sales Price field

Follow the guide below, but instead of setting the sales price on products to $0, do the following.

1.Use the "Pricelists" feature with "Advanced price rules" and create a pricelist named "Sales Price", for example, then create a rule for a 0% discount on all products. On the "Configuration" tab of the new pricelist, make sure to set the website, then use developer mode to set this pricelist as the default for new contacts as this now replaces the system default "Public Pricelist".

2. In the original "Public Pricelist", create a fixed price rule to set all products to $0. Go to the "Configuration" tab and uncheck the "Selectable" box.

https://www.odoo.com/forum/help-1/how-can-i-force-visitors-to-register-before-seeing-prices-on-an-ecommerce-website-in-odoo-16-239736

Hi, this might help you: https://youtu.be/An6YTH3kJD8

Thanks

I'm facing the same issue -- this was working in Odoo 15 like charm..... 

We need a solution for it in 16 :-)

Depending on what modules are installed, we found it in Settings -> Sale

https://github.com/odoo/odoo/blob/289589ce4918b6908144b354892a4ca1292ec27b/addons/sale/views/res_config_settings_views.xml#L138

I don't have this 'on invitation' or 'free sign up' option. 
Did it move somewhere else? 

As Kashif said... 

Odoo V16 Enterprise (On www.odoo.com)

Hello, don´t work how i need it.. Your Answer mean that no checkout without register, but i need to hide the "i have no account register (signup)". (on B2B Side is a register not usefull) It looks like that the parameter "signup_enabled" in the file auth_signup.login has no way to set/edit in the Backend.