Below are the most common reasons why a User cannot edit a Dashboard or a Report, along with resolution steps when possible:
1. Any Reports or Dashboards edited or created in Lightning Experience cannot be edited in Classic Salesforce. Even if the Report started as a Classic Salesforce report. Once it is edited in Lightning, it will remain a Lightning Report or Dashboard.
2. Can click "Edit" on a Dashboard, but on the edit screen everything is greyed out?
a. You are not the running user of the Dashboard. You may need to change the running user by clicking in the top right. Only System Admin Users can change the Running User of a Dashboard.
b. Every Dashboard component uses a Source Report to query the data displayed on the Dashboard. You do not have access to the source report for that dashboard chart data. Ask your System Administrator to Share the Report folder with you.
3. You do not have access to the folder the report/dashboard is in. On old report systems, this would be because a folder was created as private. There was no way to share the contents of the folder, besides moving reports out of the folder. By 2022, all systems should be transitioned to the new report system. The visual effect of this is nigh non-existent, so you may already be transitioned. To check and see, or even transition yourself, you can follow this article: Enable Report and Dashboard Folder Sharing
On the new report sharing system, this problem can be resolved by the owner of a report folder sharing the folder with other users via the share button, more on that here: Report Folder Sharing Options
For more info on report/dashboard folder sharing, please see the below information provided by Salesforce.
Please note that there are two distinct types of Reporting and Dashboard folder sharing. Please ensure that you are reviewing details specific to the version being utilized within your environment.
Determining whether you are using the legacy or enhanced version of the folder sharing can be done by using the below click path:
Setup > Customize > Reports & Dashboards > Folder Sharing
Here you will find a setting called "Enable access levels for sharing report and dashboard folders." If this option is populated, you are using the "Enhanced" version. Otherwise, the Legacy option is being employed.
Resolution Legacy folder sharing model
ACCESS LEVEL 1
The "Manage Dashboards" profile permission allows a user to:
Create a dashboard (in dashboard folders which they have access to)
Clone an existing dashboard
Edit a dashboard YOU CREATED only (you cannot change Running User from yourself to another user)
The user will be automatically set as the Running User and cannot be changed to any other user.
NOTE: If a user sees the "Edit" button for a dashboard they didn't create, the "Insufficient Privileges" message will display when editing.
ACCESS LEVEL 2
A profile ALSO needs "View All Data" permission to do the following:
Edit any dashboard
Set or change Running User
Create or change dashboard folders and folder permissions
Enhanced folder sharing model
In organizations using enhanced folder sharing, users can edit some dashboard details and save the changes as the current running user of the dashboard. They will be restricted to which details they can modify if they are not the running user of the dashboard. To ensure complete access, the profile permission "View All Data" must also be granted. But to use this capability, the following conditions must be met:
Enhanced Analytics Sharing must be enabled
The user must have Editor or Manager access to the dashboard's folder
The user must have the following permissions:
Create and Customize Dashboards
Manage Dashboards in Public Folders
Drag-and-Drop Dashboard Builder
Manage Dynamic Dashboards is requested to edit Dynamic Dashboards
Also big note, if you edit a dashboard in Lightning Experience, it will then be locked to only be editable in Lightning Experience.
Dashboards created in Classic can be edited in Classic.
Dashboards created in LE can be edited in LE.
Dashboards created in Classic can be edited in LE. Once the dashboard has been edited in LE it can no longer be edited in Classic.