Jekyll-default-layout noob problem

Why can’t I install the plugini jekyll 4.1.1?

$ gem install jekyll-default-layout
Successfully installed jekyll-default-layout-0.1.4
Parsing documentation for jekyll-default-layout-0.1.4
Done installing documentation for jekyll-default-layout after 0 seconds
1 gem installed

$ bundle add jekyll-default-layout
Fetching gem metadata from rubygemsorg/…
Fetching gem metadata from rubygemsorg/.
Resolving dependencies…
Bundler could not find compatible versions for gem “jekyll”:
In snapshot (Gemfile.lock):
jekyll (= 4.1.1)

In Gemfile:
jekyll (~> 4.1)

jekyll-default-layout was resolved to 0.1.0, which depends on
  jekyll (~> 3.3)

Running bundle update will rebuild your snapshot from scratch, using only
the gems in your Gemfile, which may resolve the conflict.

try instal theme: git-wiki-theme

Look at the message at the end. The default gem you are installing only works with Jekyll 3 but you have Jekyll 4.

So add jekyll 3 instead to your Gemfile and to bundle install to downgrade jekyll. Maybe delete the lock file.

Or find someone who made a variation of the gem like a fork that works for jekyll 4.

If you are using GitHub Pages without GH Actions then you should use jekyll 3.8.5 and that will solve the problem.

Unless you’re using a different flow and really need jekyll 4