It sounds like you may need to update the Ruby version that Jekyll is using. Here are some steps you can try:

Check your Ruby version:

Open a terminal or command prompt and type ruby -v to check which version of Ruby you have installed.

Install a newer version of Ruby:

If you don't have a version of Ruby 2.6.6 or higher, you can download and install it from the official Ruby website: https://www.ruby-lang.org/en/downloads/

Update your system's Ruby version:

If you already have a newer version of Ruby installed, you can update your system's default Ruby version by running sudo update-alternatives --config ruby in the terminal or command prompt. Select the version of Ruby you want to use as the default.

Install Jekyll:

Once you have the correct version of Ruby installed, you can install Jekyll by running gem install jekyll in the terminal or command prompt.

Check Jekyll version:

Type jekyll -v to confirm that Jekyll is installed and running on the correct version of Ruby.

If these steps don't work, you may want to try using a Ruby version manager like RVM or rbenv to manage your Ruby versions.