"Configuration file: none" on bundle exec jekyll serve - terminal

Question

At first I could use (not bundle exec) jekyll serve without any problem.
Then I started creating a yaml data file (still trying to make it work) and, don't know how, I "lost" the Gemfile and the Gemfile.lock.
When trying to run jekyll serve (with and without bundle exec) I got an error as result. Then I added again the Gemfile and the Gemfile.lock and got this result:
bundle exec jekyll serve
Configuration file: none
Source: /Users/..../Documents/.../My_website/...
Destination: /Users/..../Documents/.../My_website/.../_site
Incremental build: disabled. Enable with --incremental
Generating...
/Users/..../.rvm/gems/ruby-2.7.0/gems/jekyll-4.0.0/lib/jekyll/convertible.rb:41: warning: Using the last argument as keyword parameters is deprecated
/Users/..../.rvm/gems/ruby-2.7.0/gems/jekyll-4.0.0/lib/jekyll/convertible.rb:41: warning: Using the last argument as keyword parameters is deprecated
/Users/..../.rvm/gems/ruby-2.7.0/gems/jekyll-4.0.0/lib/jekyll/convertible.rb:41: warning: Using the last argument as keyword parameters is deprecated
------------------------------------------------
Jekyll 4.0.0 Please append `--trace` to the `serve` command
for any additional information or backtrace.
------------------------------------------------
Traceback (most recent call last):
29: from /Users/..../.rvm/gems/ruby-2.7.0/bin/ruby_executable_hooks:24:in `<main>'
28: from /Users/..../.rvm/gems/ruby-2.7.0/bin/ruby_executable_hooks:24:in `eval'
27: from /Users/..../.rvm/gems/ruby-2.7.0/bin/jekyll:23:in `<main>'
26: from /Users/..../.rvm/gems/ruby-2.7.0/bin/jekyll:23:in `load'
25: from /Users/..../.rvm/gems/ruby-2.7.0/gems/jekyll-4.0.0/exe/jekyll:15:in `<top (required)>'
24: from /Users/..../.rvm/gems/ruby-2.7.0/gems/mercenary-0.3.6/lib/mercenary.rb:19:in `program'
23: from /Users/..../.rvm/gems/ruby-2.7.0/gems/mercenary-0.3.6/lib/mercenary/program.rb:42:in `go'
22: from /Users/..../.rvm/gems/ruby-2.7.0/gems/mercenary-0.3.6/lib/mercenary/command.rb:220:in `execute'
21: from /Users/..../.rvm/gems/ruby-2.7.0/gems/mercenary-0.3.6/lib/mercenary/command.rb:220:in `each'
20: from /Users/..../.rvm/gems/ruby-2.7.0/gems/mercenary-0.3.6/lib/mercenary/command.rb:220:in `block in execute'
19: from /Users/..../.rvm/gems/ruby-2.7.0/gems/jekyll-4.0.0/lib/jekyll/commands/serve.rb:86:in `block (2 levels) in init_with_program'
18: from /Users/..../.rvm/gems/ruby-2.7.0/gems/jekyll-4.0.0/lib/jekyll/command.rb:89:in `process_with_graceful_fail'
17: from /Users/..../.rvm/gems/ruby-2.7.0/gems/jekyll-4.0.0/lib/jekyll/command.rb:89:in `each'
16: from /Users/..../.rvm/gems/ruby-2.7.0/gems/jekyll-4.0.0/lib/jekyll/command.rb:89:in `block in process_with_graceful_fail'
15: from /Users/..../.rvm/gems/ruby-2.7.0/gems/jekyll-4.0.0/lib/jekyll/commands/build.rb:36:in `process'
14: from /Users/..../.rvm/gems/ruby-2.7.0/gems/jekyll-4.0.0/lib/jekyll/commands/build.rb:65:in `build'
13: from /Users/..../.rvm/gems/ruby-2.7.0/gems/jekyll-4.0.0/lib/jekyll/command.rb:28:in `process_site'
12: from /Users/..../.rvm/gems/ruby-2.7.0/gems/jekyll-4.0.0/lib/jekyll/site.rb:74:in `process'
11: from /Users/..../.rvm/gems/ruby-2.7.0/gems/jekyll-4.0.0/lib/jekyll/site.rb:174:in `read'
10: from /Users/..../.rvm/gems/ruby-2.7.0/gems/jekyll-4.0.0/lib/jekyll/reader.rb:19:in `read'
9: from /Users/..../.rvm/gems/ruby-2.7.0/gems/jekyll-4.0.0/lib/jekyll/readers/data_reader.rb:20:in `read'
8: from /Users/..../.rvm/gems/ruby-2.7.0/gems/jekyll-4.0.0/lib/jekyll/readers/data_reader.rb:38:in `read_data_to'
7: from /Users/..../.rvm/gems/ruby-2.7.0/gems/jekyll-4.0.0/lib/jekyll/readers/data_reader.rb:38:in `each'
6: from /Users/..../.rvm/gems/ruby-2.7.0/gems/jekyll-4.0.0/lib/jekyll/readers/data_reader.rb:46:in `block in read_data_to'
5: from /Users/..../.rvm/gems/ruby-2.7.0/gems/jekyll-4.0.0/lib/jekyll/readers/data_reader.rb:66:in `read_data_file'
4: from /Users/..../.rvm/gems/ruby-2.7.0/gems/safe_yaml-1.0.5/lib/safe_yaml/load.rb:157:in `load_file'
3: from /Users/..../.rvm/gems/ruby-2.7.0/gems/safe_yaml-1.0.5/lib/safe_yaml/load.rb:157:in `open'
2: from /Users/..../.rvm/gems/ruby-2.7.0/gems/safe_yaml-1.0.5/lib/safe_yaml/load.rb:157:in `block in load_file'
1: from /Users/..../.rvm/gems/ruby-2.7.0/gems/safe_yaml-1.0.5/lib/safe_yaml/load.rb:143:in `load'
/Users/..../.rvm/gems/ruby-2.7.0/gems/safe_yaml-1.0.5/lib/safe_yaml/load.rb:143:in `parse': (/Users/..../Documents/_VITO/My_website/website2020/_data/audio.yaml): mapping values are
not allowed in this context at line 8 column 11 (Psych::SyntaxError)
The project has a config.yaml and both Gemfile and Gemfile.lock. I don't know what Configuration file: none would mean.
That's what my Gemfile looks like:
# frozen_string_literal: true
source "https://rubygems.org"
git_source(:github) {|repo_name| "https://github.com/#{repo_name}" }
# gem "rails"
gem "jekyll", "~> 4.0"
I am sure I made pretty much a mess (first timer with Jekyll) and hope you can help me.

Answer 1

bundle add webrick
this worked for me on windows 10

Answer 2

When making changes to the file (index.html), add a blank front matter (two triple-dashed lines at the start of a file ), it will work.
You don't need to see Gemfile at the moment.