I have created three websites within a single Magento instance.
All three store is showing in configuration it means are enable and active.
I have put Magento version
2.3.3 with sample data.
When I Create/Edit product admin show only one website view which is a default.
You need to follow below steps :
And there is only one website is assigned which is default. I just recently created new website "Demo" that is not assigned there.
So please select new website checkbox and save that product and then check that dropdown. Please check below screenshot.
Now I can see that website is available in that dropdown.
So if you want to assign all products then go to Product's Grid and then select all products and select action "Update Attributes". There is one tab available called "Websites", click on that and select your new website's checkbox there. Please check below screenshot.
And click on "Save button".
After that please run below command once
php bin/magento indexer:reindex php bin/magento cache:clean php bin/magento cache:flush
Hope this will help you!
Before using the New Product function and page, you must first visit the configuration page for the Site that you want the product to pertain to.
Stores > All Stores > [select Web Site] >
On that config page, check the Set as Default button.
Now start the Add New Product process.
Way down the Product configuration page there's a setting for "Product in Websites", on which you can set which Websites the product is available on. (And not to be confused with the Categories setting and mechanism.)
It looks like the "Set as Default" (Website) preselects that Website in the "Product in Websites" settings.
You can use "Product in Websites" to add one or more additional sites. After saving that setting, the product config page will then display a Scope control at top left, including scopes for those sites.