By default the CKEditor 5 does not offer the option to change fonts. You can fix that by following the steps described here.
First install the CKEditor Font Size and Family module.
The composer command is:
composer require 'drupal/ckeditor_font:^2.0@beta'
Verify if the module is abailable using Drush:
./vendor/bin/drush pm:list | grep CK
Enable the module with Drush:
./vendor/bin/drush pm:enable ckeditor_font
After you have enabled the module, navigate to: /admin/config/content/formats/ and select your text format to configure it.
You should see these new icons appear inside the toolbar configuration.
Drag the icons into your active toolbar in order to active them. Don't forget to save your configuration.
You can now change font family, size and colours inside CKEditor 5 in your Drupal 10 website.