Hi @Pritam Das ,
Welcome to the community!
Removing "The Service Desk Customer - Portal Access" from the project permission scheme is not advisable. The way to allow users (or customers with restricted portal access) to only see the Service Desk project(s) they are assigned to, is the following:
Repeat above steps for each Service Desk project and provide your customers with a single URL to find a list of all the customer portals they can access and the requests they created in each one: https://<instance_name>.atlassian.net/servicedesk/customer/portals
EXTENSION TO STEPS 2 AND 3:
If you have a lot of restricted users and you don't want to add them one by one then you can uncheck the "Restricted Portal Access" checkbox for those users. This way the users will not be using any licence since they don't have any application access and you will be able to add them to groups. On the other hand you have to be really careful when doing this because if, by mistake, you give application access to one of these groups then you will be using a lot of licences.
For further details on this please see below documentation:
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