Drupal 9, How to solve “Mismatched entity and/or field definitions”

It’s very common to find this warning in the status report page of a Drupal site, this happens usually on the development phase while we are adding/removing fields and modules.

In order to solve this issue staring in Drupal 8.7 and above you need to install a contrib module called Devel Entity Updates

As it says in the module doc

This command is a drop-in replacement of the legacy drush entup or drush entity-updates core commands, however drush updb --entity-updates is no longer supported. Just run the drush entup command as before.

Just enable the module and run drush entup to fix these fields issues.