Explanation
There are two possible reasons why users are unable to access a report based on a custom report type created by an administrator. One is that the custom report type is in development mode, which means that it is not deployed and available for use by other users except for administrators and users with manage custom report types permission. The other is that the report is saved in a private folder, which means that it is visible only to its owner and not shared with other users or groups. References:
https://help.salesforce.com/s/articleView?id=sf.reports_builder_custom_report_types.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.reports_builder_folders.htm&type=5

Explanation
Auto response rules are a way to automatically send email responses to leads or cases based on certain criteria such as lead source, industry, etc. They can be used to send personalized emailswhenever a lead fills out a web-to-lead form on a website and send different messages based on the lead industry field value. Using validation rule to trigger workflow to email the lead is not possible because validation rules cannot trigger workflows or send emails; they only prevent records from being saved if they do not meet certain criteria.
Adding a public group and process builder to email the lead is unnecessary because auto response rules can handle this requirement without additional configurationor customization. Creating an assignment rule to email the lead is also unnecessary because assignment rules are used to assign leads or cases to users or queues based on certain criteria, not send emails; although they can have email alerts as part of their actions, they are not as flexible as auto response rules for personalizing email messages.
References:https://help.salesforce.com/s/articleView?id=sf.customize_leadsautoresponse.htm&type=5

Explanation
To make a tab hidden in the All App Launcher or visible inany app, but still allow a user to view records that would normally be found under this tab, the administrator should use Tab Settings on a profile. Tab Settings control the visibility and default behavior of tabs for each app in an org. The administratorcan set a tab to Hidden, which means it will not appear in any app or in the All App Launcher, but users can still access records via other means such as search or reports. Object Permissions, App Permissions, and Org-Wide Defaults are not related to tabvisibility.
References:https://help.salesforce.com/s/articleView?id=sf.customize_tabs.htm&type=5

Explanation
A Trailhead Playground is a free, online learning environment that allows you to try out Salesforce features and apps. You can use a Trailhead Playground to test out an app from the AppExchange before you install it in your production org.
A sandbox is a copy of your production org that you can use to test changes and new features. You can install an app from the AppExchange in a sandbox to see how it works in your environment.
Testing an app in a production org is not recommended, as it could affect your live data. Checking edition compatibility is important, but it is not a way to try out an app.