Change record status: 
Project: 
Introduced in branch: 
9.4.x
Introduced in version: 
9.4.0
Description: 

The support for forbidden_tags in FilterFormat::getHtmlRestrictions() (which computes the cumulative HTML restrictions of all filters in the text format) has always been broken, which means nobody could've been using it.

Nobody ever reported this bug in the entire lifespan of Drupal 8 and 9. Hence it was decided to deprecate this in Drupal 9.4.x and remove it in Drupal 10.0.x.

Impacts: 
Module developers