What was once only available in the Classic version is now available in Salesforce Lightning thanks to the Spring’21 Release. It is a Sharing button that allows you to share information with any user in the Salesforce organization.
On the example of a record on the Business Opportunity object, on the right side we expand the list of available actions, click the Sharing button to grant access to this record
After clicking, the editing sharing window will open and in the first field we can choose which user or group of users we want to grant access to.
Then we define what permissions will be granted to people with access to our record.
Read Only – read-only access to information.
Read / Write – the ability to edit data.
By clicking the Edit button, we can manage users who have access to the record, delete, change permissions, and using the View Sharing hierarchy button, we have access to the full list of people who have access to the data.