An in-between solution for you might be:

def initialize(site:, name:, **options)
  @site          = site
  @name          = name
  @date_online   = options[:date_online]   || '-'
  @date_offline  = options[:date_offline]  || '-'
  @date_modified = options[:date_modified] || '-'
  @date_tagged   = options[:date_tagged]   || '-'
  @tags          = options[:tags]          || []
end

You would probably want to raise an error if an unexpected key was passed in as part of options.

An in-between solution for you might be:

def initialize(site:, name:, **options)
  @site          = site
  @name          = name
  @date_online   = options[:date_online]   || '-'
  @date_offline  = options[:date_offline]  || '-'
  @date_modified = options[:date_modified] || '-'
  @date_tagged   = options[:date_tagged]   || '-'
  @tags          = options[:tags]          || []
end

You would probably want to raise an error if an unexpected key was passed in as part of options.