Reddit can restore your deleted posts. However, if people flood them with GDPR / CCPA delete requests, they may become liable for lawsuits if they don’t comply.
It sounds like their current policy is to not delete your posts even when deleting your account, but there may be grounds for legal action here.
It doesnt’ belong to Reddit. You give them a license (transferrable and non-revocable) to use the content. But in the EU that is superceded by the GDPR.