Name tags missing post upgrade?

If you have performed face recognition in a prior version and have applied People tag names to your photos, you should convert the prior version's catalog for use in Elements 2021.  You were given the opportunity to convert the catalog when you first launched Elements 2021, but perhaps you missed it.  So, if this is the situation, I suggest that you convert the old catalog now and all of your existing name tags will be there.  To do this, go to File>Manage Catalogs and click on the Convert button.  Your old catalog should show up in a dialog box.  Select it, then click the Convert button.

If this is not what happened, please let us know how you have created a catalog in Elements 2021.  Did you import all of your files using one of the options in the Import menu?  If so, were you given the opportunity to import any tags that have been saved in the file's metadata.  In that case, the People tags will appear as regular keyword tags and will appear in the category for Imported Keywords.  Although it is possible to turn these keyword tags into People tags, it is labor intensive and all of the face recognition work you have performed will have been lost.  For these reasons, it is far better to convert the old catalog.

For more details, see this HelpX Article.