App (rails 6.1.1) can't boot after upgrading to Ruby 3.0 – Debian

Here is the Gemfile:

source 'https://rubygems.org'
git_source(:github) { |repo| "https://github.com/#{repo}.git" }

ruby '3.0.0'

# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '~> 6.1.0'
# Use mysql as the database for Active Record
gem 'mysql2', '>= 0.4.4'
# Use Puma as the app server
gem 'puma', '~> 5.0'
# Use SCSS for stylesheets
gem 'sass-rails', '>= 6'
# Transpile app-like JavaScript. Read more: https://github.com/rails/webpacker
gem 'webpacker', '~> 5.0'
# Turbolinks makes navigating your web application faster. Read more: https://github.com/turbolinks/turbolinks
gem 'turbolinks', '~> 5'
# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder', '~> 2.7'

# Flexible authentication solution for Rails with Warden
gem 'devise', '~> 4.7'

# A simple HTTP and REST client
gem 'rest-client', '~> 2.1'

# Reduces boot times through caching; required in config/boot.rb
gem 'bootsnap', '>= 1.4.2', require: false

# Devise supports i18n in controllers, models, and in other areas,
# but it does not have support for internationalized views.
# devise-i18n adds this support.
gem 'devise-i18n', '~> 1.9'
# Devise Bootstrap Views
gem 'devise-bootstrap-views', '~> 1.0'
# Configure Devise to send its emails asynchronously using ActiveJob
gem 'devise-async', '~> 1.0'

# Stripe is the easiest way to accept payments online
gem 'stripe', '~> 5.22'

# A gem that provides a client interface for the Sentry error logger
gem 'sentry-raven', '~> 3.0'

# Taming Rails' Default Request Logging
gem 'lograge', '~> 0.11'

# Ruby state machines
gem 'aasm', '~> 5.0'
# Allows to use ActiveRecord transactional callbacks outside of ActiveRecord models, literally everywhere in your application.
gem 'after_commit_everywhere', '~> 0.1', '>= 0.1.5'

# Agnostic pagination in plain ruby
gem 'pagy', '~> 3.8'

# Connection Pool
gem 'connection_pool', '~> 2.2'

# Redis client
gem 'hiredis', '~> 0.6'
gem 'redis', '~> 4.1', require: ['redis', 'redis/connection/hiredis']

# Sidekiq
gem 'sidekiq', '~> 6.0'

# Check password strength against several rules
gem 'password_strength', '~> 1.1'

# Slack Ruby Client
gem 'slack-ruby-client', '~> 0.15'

# Assets on AWS S3/CloudFront
gem 'asset_sync', '~> 2.12'
gem 'fog-aws', '~> 3.6'

group :development, :test do
  # Call 'byebug' anywhere in the code to stop execution and get a debugger console
  gem 'byebug', platforms: [:mri, :mingw, :x64_mingw]
end

group :development do
  # Access an interactive console on exception pages or by calling 'console' anywhere in the code.
  gem 'web-console', '>= 3.3.0'
  gem 'listen', '>= 3.0.5'
  # Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
  gem 'spring'
  gem 'spring-watcher-listen', '~> 2.0'
  gem 'rspec-rails', '~> 4.0'
  gem 'amazing_print', '~> 1.2'
end

group :test do
  # Adds support for Capybara system testing and selenium driver
  gem 'capybara', '>= 2.15'
  gem 'capybara-screenshot'
  gem 'selenium-webdriver'
  # Easy installation and use of web drivers to run system tests with browsers
  gem 'webdrivers'
  gem 'factory_bot_rails', '~> 6.0'
  gem 'shoulda-matchers', '~> 4.1'
  gem 'rails-controller-testing'
  gem 'faker'
  gem 'database_cleaner-active_record'
  gem 'coderay'
  gem 'mock_redis'
end

The application seems to be blocked during Rails.application.initialize!.
I wonder if it could be a gem that is not compatible with Ruby 3.0, but I started a new app from scratch, installed all the gems and the app started normally.

I’m using puma (5.1.1) as web server.
The app is running in docker container via docker-compose.

FROM ruby:2.7.2

# Update for security reason
RUN apt-get update -yqq && apt-get upgrade -yqq -o Dpkg::Options::="--force-confold" && apt-get install -yqq --no-install-recommends 
  vim # needed for editing rails credentials

# Ensure we install an up-to-date version of Node
RUN curl -sL https://deb.nodesource.com/setup_14.x | bash -

# Ensure latest packages for Yarn
RUN curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add -
RUN echo "deb https://dl.yarnpkg.com/debian stable main" | tee /etc/apt/sources.list.d/yarn.list

RUN apt-get update -yqq && apt-get install -yqq --no-install-recommends 
  nodejs 
  yarn

ENV RAILS_ROOT /var/www/app
RUN mkdir -p $RAILS_ROOT

COPY Gemfile* /var/www/app/
WORKDIR /var/www/app

ENV BUNDLE_PATH /gems

RUN bundle install

COPY package.json package.json
COPY yarn.lock yarn.lock

RUN yarn install --check-files

COPY . /var/www/app/

EXPOSE 3000

# Clean up APT when done.
RUN apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*

ENTRYPOINT ["./puma-entrypoint.sh"]
CMD ["bundle", "exec", "puma", "-C", "config/puma/development.rb"]

# Puma can serve each request in a thread from an internal thread pool.
# The `threads` method setting takes two numbers: a minimum and maximum.
# Any libraries that use thread pools should be configured to match
# the maximum value specified for Puma. Default is set to 5 threads for minimum
# and maximum; this matches the default thread size of Active Record.
#
max_threads_count = ENV.fetch("RAILS_MAX_THREADS") { 5 }
min_threads_count = ENV.fetch("RAILS_MIN_THREADS") { max_threads_count }
threads min_threads_count, max_threads_count

# Specifies the `worker_timeout` threshold that Puma will use to wait before
# terminating a worker in development environments.
#
worker_timeout 3600 if ENV.fetch("RAILS_ENV", "development") == "development"

# Specifies the `port` that Puma will listen on to receive requests; default is 3000.
#
port ENV.fetch("PORT") { 3000 }

# Specifies the `environment` that Puma will run in.
#
environment ENV.fetch("RAILS_ENV") { "development" }

# Specifies the `pidfile` that Puma will use.
pidfile ENV.fetch("PIDFILE") { "tmp/pids/server.pid" }

# Specifies the number of `workers` to boot in clustered mode.
# Workers are forked web server processes. If using threads and workers together
# the concurrency of the application would be max `threads` * `workers`.
# Workers do not work on JRuby or Windows (both of which do not support
# processes).
#
# workers ENV.fetch("WEB_CONCURRENCY") { 2 }

# Use the `preload_app!` method when specifying a `workers` number.
# This directive tells Puma to first boot the application and load code
# before forking the application. This takes advantage of Copy On Write
# process behavior so workers use less memory.
#
# preload_app!

# Allow puma to be restarted by `rails restart` command.
plugin :tmp_restart

Is there a way to have logs to see what is happening during boot process?