Hi @rr-4098,
Thanks for your information.
Here is my database for test.

I checked the database properties, it has my domain\user account as the owner, because I created it.

Then I created a Test account with login to allow me to connect into SQL Server (Using SQL Authentication and the Test login)

During I created the account, I Use the server level login (Test) to set its Mappings to include the Test database.

Here you can see what my Test sees at the server level (everything) while it throws an error if I try to access any database.

However, when Test tries to access a database that it is mapped to, it can see the objects inside that database that have been granted to it under database user's Securable permissions.

Please feel free to share the issue more detailed here If you have any other questions, thank you.
Best regards,
Lucy Chen
If the answer is the right solution, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our Documentation to enable e-mail notifications if you want to receive the related email notification for this thread.
https://docs.microsoft.com/en-us/answers/support/email-notifications