Static Jekyll static application is now not compiling

I created a App with my Jekyll static application on github. The application compiles locally and compiled in April but now it doesn’t compile. Error [2022-07-06 00:56:56] Running custom build command: bundle exec jekyll build -d ./public [2022-07-06 00:56:57] bundler: failed to load command: jekyll (/layers/heroku_ruby/gems/vendor/bundle/ruby/3.1.0/bin/jekyll) [2022-07-06 00:56:57] /layers/heroku_ruby/gems/vendor/bundle/ruby/3.1.0/gems/bundler-2.3.10/lib/bundler/definition.rb:481:in `materialize’: Could not find rake-13.0.3 in any of the sources (Bundler::GemNotFound)

The Digital Ocean example https://github.com/digitalocean/sample-jekyll does work

I am not very knowledgable on Ruby nor Jekyll.

Any help or pointers would be appreciated.

Thanks