app/views/layouts/rails_admin/modal.js.erb
<% flash && flash.each do |key, value| %>
<div class="<%= flash_alert_class(key) %> alert alert-dismissible">
<%= value %>
<button type="button" class="btn-close" data-bs-dismiss="alert" aria-label="Close"></button>
</div>
<% end %>
<%= yield %>