Uninstall allowed_formats after D10.1 upgrade?

From the module page:

Important updates in the 3.0.0 release (3.0.x branch)

• Since Drupal 10.1.0, limiting the text formats per field instance is a feature provided by Drupal core. Read https://www.drupal.org/node/3318572 → for details.
• In the 3.0.0 release, the allowed formats feature has been removed as obsolete, but we provide an update path from existing sites to move the allowed formats, as they were stored by the previous versions of the module, to Drupal >=10.1.0 way, in field settings.
• The module provides also a feature that allows site builders to hide the formatted text format help and guidelines. Even this feature is still preserved in the 3.0.x module branch, there is an issue that aims to move it in Drupal core in the future. See https://www.drupal.org/i/3323007 → .

So it depends if you use the feature of this module to hide the formatted text format help and guidelines. That functionality isn't in Core yet.

If you aren't sure whether a site uses the feature, uninstall the module and export site config in a dev environment. If a config file besides core.extension.yml was changed, then the module was still used.