I am going to explain how we can create labels for retention policies at the tenant level so that labels can be applicable across site collections.
Click on Admin. Admin is visible to the tenant administrators only and not to site collection administrators.
After that, expand the Admin center and click on "Security & Compliance".
Then, click on "Go to the governance dashboard".
Click on "Create Label" as shown below.
Name your label as shown below and click "Next".
In label settings, we choose from the options what should happen after 10 years of document creation. Below is the screenshot.
Click on the Next button once the settings are finalized. Finally, you can review your settings and click "Create this label".
Once the Label is created, we have the option to publish it. Click on "Publish" as shown below.
This is how we can publish labels. Follow the next step.
Click on Next as shown in the screenshot above. In the below screen, we can choose to publish the Label to all or we choose specific locations depending upon the requirement.
Click "Next" as shown above.
Give a friendly name to your policy as shown below.
Review your settings and publish labels as shown below.
Below, we can see that the status shows pending. You can also edit or delete it.
After some time (I checked it after 30 minutes), the Status is changed to successful.
We can apply labels by going to the Library Settings.
Click on "Apply label to items in this list or library", as in the below screen. Select a label and it will apply to each document in the library.