Azure App Service is a service used to create and deploy scalable, mission-critical web apps.
@yuya , Thanks for the question.
Are you using private or public GitHub repo?
Kindly set the Application setting- SCM_ENABLE_DYNAMIC_INSTALL=false for PHP 7.4 -and then check.
For more information - https://github.com/projectkudu/kudu/wiki/Configurable-settings