My order emails and XML sitemap stopped generating, is that a cron problem?

Almost always, yes. Order/transactional emails are queued and sent by the message-queue consumers, and the XML sitemap is generated by a scheduled cron job, both die silently when cron is dead or its consumers are not running. We restore cron:run, confirm the consumers_runner config and the sitemap / email cron jobs, then trigger a regeneration so the backlog clears.