I used sudo bundle install and that might be the cause of the issue?
Now I have:
gem -v 2.6.14ruby -v
The problem in my case is that the Gemfile.lock file had a BUNDLED_WITH version of 1.16.1 and gem install bundler installed version 2.0.1, so there was a version mismatch when looking to right the folder
gem install bundler -v 1.16.1 fixed it
Of course, you can also change your Gemfile.lock's BUNDLED_WITH with last bundler version and use recent software, as Sam3000 suggests