After upgrading to Flask 2.0, usingapp.config.from_json() gives the following error:

AttributeError: 'Config' object has no attribute 'from_json'

The changelog only says that it has been deprecated, but not removed:

AddConfig.from_file() to load config using arbitrary file loaders, such astoml.load orjson.load.Config.from_json() is deprecated in favor of this.#3398